It's starting to "properly" reply...

The ACSL coverage is far behind though.

37 files changed, 1148 insertions, 387 deletions

diff --git a/doc/protocol.txt b/doc/protocol.txt
index f29885c..bceaa97 100644
--- a/doc/protocol.txt
+++ b/doc/protocol.txt
@@ -14,14 +14,13 @@ allowed to contain the character '\n'.
 ######## Request Protocol Version ##############################################
 ########## Syntax
 "<TAG>": "?RPV"
-"<CONTENT>": list of comma separated unsigned integers.
+"<CONTENT>": list of comma separated unsigned integers, in a ascending order.
 
 ########## Semantic
 Upon reception of one such message, one should start using the latest
 Zero of One protocol version listed in <CONTENT> that one can. If none are
-supported, communication sockets should be closed (error messages may be sent
-prior to closing the socket). Otherwise, a Confirm Protocol Version message
-should be sent.
+supported, a Negative reply is sent. Otherwise, a Confirm Protocol Version
+message should be sent.
 
 ######## Request Learn #########################################################
 ########## Syntax
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 25cacc2..33a89cf 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,7 +1,7 @@
 add_subdirectory(core)
+add_subdirectory(error)
 add_subdirectory(knowledge)
 add_subdirectory(parameters)
-add_subdirectory(pipe)
 add_subdirectory(sequence)
 add_subdirectory(server)
 add_subdirectory(storage)
diff --git a/src/core/char.c b/src/core/char.c
index 819cd57..a6b3c8d 100644
--- a/src/core/char.c
+++ b/src/core/char.c
@@ -18,9 +18,30 @@ int ZoO_word_cmp
 (
    const ZoO_char word_a [const static 1],
    const size_t word_a_size,
-   const ZoO_char word_b [const static 1]
+   const ZoO_char word_b [const static 1],
+   const size_t word_b_size
 )
 {
-   return strncmp((const char *) word_a, (const char *) word_b, word_a_size);
+   int result;
+   size_t min_size;
+
+   if (word_a_size < word_b_size)
+   {
+      result =
+         strncmp((const char *) word_a, (const char *) word_b, word_a_size);
+
+      return (result == 0) ? -1 : result;
+   }
+   else if (word_b_size < word_a_size)
+   {
+      result =
+         strncmp((const char *) word_a, (const char *) word_b, word_b_size);
+
+      return (result == 0) ? 1 : result;
+   }
+   else
+   {
+      return strncmp((const char *) word_a, (const char *) word_b, word_a_size);
+   }
 }
 
diff --git a/src/core/char.h b/src/core/char.h
index 7039563..69606a0 100644
--- a/src/core/char.h
+++ b/src/core/char.h
@@ -13,7 +13,8 @@ int ZoO_word_cmp
 (
    const ZoO_char word_a [const static 1],
    const size_t word_a_size,
-   const ZoO_char word_b [const static 1]
+   const ZoO_char word_b [const static 1],
+   const size_t word_b_size
 );
 
 /*
diff --git a/src/core/state_types.h b/src/core/state_types.h
deleted file mode 100644
index 89c814e..0000000
--- a/src/core/state_types.h
+++ /dev/null
@@ -1,16 +0,0 @@
-#ifndef _ZoO_CORE_STATE_TYPES_H_
-#define _ZoO_CORE_STATE_TYPES_H_
-
-#include "../io/parameters_types.h"
-#include "../io/network_types.h"
-
-#include "knowledge_types.h"
-
-struct ZoO_state
-{
-   struct ZoO_parameters param;
-   struct ZoO_knowledge knowledge;
-   struct ZoO_network network;
-};
-
-#endif
diff --git a/src/pipe/CMakeLists.txt b/src/error/CMakeLists.txt
index fa07534..fa07534 100644
--- a/src/pipe/CMakeLists.txt
+++ b/src/error/CMakeLists.txt
diff --git a/src/pipe/pipe.h b/src/error/error.h
index 4616050..9a7fe04 100644
--- a/src/pipe/pipe.h
+++ b/src/error/error.h
@@ -1,12 +1,10 @@
-#ifndef _ZoO_PIPE_PIPE_H_
-#define _ZoO_PIPE_PIPE_H_
+#ifndef _ZoO_ERROR_ERROR_H_
+#define _ZoO_ERROR_ERROR_H_
 
 #include <stdio.h>
 
 #include "../pervasive.h"
 
-#include "pipe_types.h"
-
 #ifndef ZoO_DEBUG_PROGRAM_FLOW
    #define ZoO_DEBUG_PROGRAM_FLOW   (0 || ZoO_DEBUG_ALL)
 #endif
@@ -33,13 +31,13 @@
 #define ZoO_ENABLE_FATAL_ERROR_OUTPUT           1
 
 #ifdef ZoO_ENABLE_ERROR_LOCATION
-   #define ZoO_LOCATION "[" __FILE__ "][" ZoO_TO_STRING(__LINE__) "]"
+   #define ZoO_LOCATION " [" __FILE__ "][" ZoO_TO_STRING(__LINE__) "]"
 #else
    #define ZoO_LOCATION ""
 #endif
 
-#define ZoO_PRINT_STDERR(pipe, symbol, str, ...)\
-   fprintf(pipe->out, "[" symbol "] " ZoO_LOCATION " " str "\n", __VA_ARGS__);
+#define ZoO_PRINT_STDERR(io, symbol, str, ...)\
+   fprintf(io, "[" symbol "]" ZoO_LOCATION " " str "\n", __VA_ARGS__);
 
 /*
  * Given that we use preprocessor contants as flags, we can expect the compilers
@@ -47,99 +45,99 @@
  * allowing many debug options.
  */
 
-#define ZoO_DEBUG(pipe, flag, str, ...)\
+#define ZoO_DEBUG(io, flag, str, ...)\
    ZoO_ISOLATE\
    (\
       if (flag)\
       {\
-         ZoO_PRINT_STDERR(pipe, "D", str, __VA_ARGS__);\
+         ZoO_PRINT_STDERR(io, "D", str, __VA_ARGS__);\
       }\
    )
 
 
-#define ZoO_WARNING(pipe, str, ...)\
+#define ZoO_WARNING(io, str, ...)\
    ZoO_ISOLATE\
    (\
       if (ZoO_ENABLE_WARNINGS_OUTPUT)\
       {\
-         ZoO_PRINT_STDERR(pipe, "W", str, __VA_ARGS__);\
+         ZoO_PRINT_STDERR(io, "W", str, __VA_ARGS__);\
       }\
    )
 
-#define ZoO_ERROR(pipe, str, ...)\
+#define ZoO_ERROR(io, str, ...)\
    ZoO_ISOLATE\
    (\
       if (ZoO_ENABLE_RUNTIME_ERRORS_OUTPUT)\
       {\
-         ZoO_PRINT_STDERR(pipe, "E", str, __VA_ARGS__);\
+         ZoO_PRINT_STDERR(io, "E", str, __VA_ARGS__);\
       }\
    )
 
-#define ZoO_PROG_ERROR(pipe, str, ...)\
+#define ZoO_PROG_ERROR(io, str, ...)\
    ZoO_ISOLATE\
    (\
       if (ZoO_ENABLE_PROGRAMMING_ERRORS_OUTPUT)\
       {\
-         ZoO_PRINT_STDERR(pipe, "P", str, __VA_ARGS__);\
+         ZoO_PRINT_STDERR(io, "P", str, __VA_ARGS__);\
       }\
    )
 
-#define ZoO_FATAL(pipe, str, ...)\
+#define ZoO_FATAL(io, str, ...)\
    ZoO_ISOLATE\
    (\
      if (ZoO_ENABLE_FATAL_ERROR_OUTPUT)\
       {\
-         ZoO_PRINT_STDERR(pipe, "F", str, __VA_ARGS__);\
+         ZoO_PRINT_STDERR(io, "F", str, __VA_ARGS__);\
       }\
    )
 
 /* For outputs without dynamic content (static). ******************************/
 
-#define ZoO_PRINT_S_STDERR(pipe, symbol, str)\
-   fprintf(pipe->out, "[" symbol "] " ZoO_LOCATION " " str "\n");
+#define ZoO_PRINT_S_STDERR(io, symbol, str)\
+   fprintf(io, "[" symbol "]" ZoO_LOCATION " " str "\n");
 
-#define ZoO_S_DEBUG(pipe, flag, str)\
+#define ZoO_S_DEBUG(io, flag, str)\
    ZoO_ISOLATE\
    (\
       if (flag)\
       {\
-         ZoO_PRINT_S_STDERR(pipe, "D", str);\
+         ZoO_PRINT_S_STDERR(io, "D", str);\
       }\
    )
 
-#define ZoO_S_WARNING(pipe, str)\
+#define ZoO_S_WARNING(io, str)\
    ZoO_ISOLATE\
    (\
       if (ZoO_ENABLE_WARNINGS_OUTPUT)\
       {\
-         ZoO_PRINT_S_STDERR(pipe, "W", str);\
+         ZoO_PRINT_S_STDERR(io, "W", str);\
       }\
    )
 
-#define ZoO_S_ERROR(pipe, str)\
+#define ZoO_S_ERROR(io, str)\
    ZoO_ISOLATE\
    (\
       if (ZoO_ENABLE_RUNTIME_ERRORS_OUTPUT)\
       {\
-         ZoO_PRINT_S_STDERR(pipe, "E", str);\
+         ZoO_PRINT_S_STDERR(io, "E", str);\
       }\
    )
 
-#define ZoO_S_PROG_ERROR(pipe, str)\
+#define ZoO_S_PROG_ERROR(io, str)\
    ZoO_ISOLATE\
    (\
       if (ZoO_ENABLE_PROGRAMMING_ERRORS_OUTPUT)\
       {\
-         ZoO_PRINT_S_STDERR(pipe, "P", str);\
+         ZoO_PRINT_S_STDERR(io, "P", str);\
       }\
    )
 
-#define ZoO_S_FATAL(pipe, str)\
+#define ZoO_S_FATAL(io, str)\
    ZoO_ISOLATE\
    (\
      if (ZoO_ENABLE_FATAL_ERROR_OUTPUT)\
       {\
-         ZoO_PRINT_S_STDERR(pipe, "F", str);\
+         ZoO_PRINT_S_STDERR(io, "F", str);\
       }\
    )
 #endif
diff --git a/src/knowledge/knowledge.c b/src/knowledge/knowledge.c
index 5ce6917..e7d1cd9 100644
--- a/src/knowledge/knowledge.c
+++ b/src/knowledge/knowledge.c
@@ -3,7 +3,7 @@
 #include <stdio.h>
 #include <stdint.h> /* defines SIZE_MAX */
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "knowledge.h"
 
@@ -13,6 +13,7 @@
 int ZoO_knowledge_initialize (struct ZoO_knowledge k [const restrict static 1])
 {
    int error;
+   ZoO_index reserved_word_id;
 
    k->words = (struct ZoO_knowledge_word *) NULL;
    k->words_length = 0;
@@ -36,25 +37,83 @@ int ZoO_knowledge_initialize (struct ZoO_knowledge k [const restrict static 1])
       return -1;
    }
 
+   if
+   (
+      (
+         ZoO_knowledge_learn_word
+         (
+            k,
+            "[SoS]",
+            5,
+            &reserved_word_id,
+            stderr
+         ) < 0
+      )
+      ||
+      (
+         ZoO_knowledge_learn_word
+         (
+            k,
+            "[EoS]",
+            5,
+            &reserved_word_id,
+            stderr
+         ) < 0
+      )
+   )
+   {
+      ZoO_S_FATAL(stderr, "Unable to learn reserved words.");
+
+      return -1;
+   }
+
    return 0;
 }
 
 int ZoO_knowledge_lock_access
 (
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
-   return pthread_mutex_lock(&(k->mutex));
+   int err;
+
+   err = pthread_mutex_lock(&(k->mutex));
+
+   if (err != 0)
+   {
+      ZoO_ERROR
+      (
+         io,
+         "Unable to get exclusive access to knowledge: %s",
+         strerror(err)
+      );
+
+      return -1;
+   }
+
+   return 0;
 }
 
 void ZoO_knowledge_unlock_access
 (
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
-   pthread_mutex_unlock(&(k->mutex));
+   int err;
+
+   err = pthread_mutex_unlock(&(k->mutex));
+
+   if (err != 0)
+   {
+      ZoO_ERROR
+      (
+         io,
+         "Unable to release exclusive access to knowledge: %s",
+         strerror(err)
+      );
+   }
 }
 
 void ZoO_knowledge_get_word
@@ -68,3 +127,37 @@ void ZoO_knowledge_get_word
    *word = k->words[word_ref].word;
    *word_length = k->words[word_ref].word_length;
 }
+
+int ZoO_knowledge_rarest_word
+(
+   const struct ZoO_knowledge k [const static 1],
+   const ZoO_index sequence [const restrict static 1],
+   const size_t sequence_length,
+   ZoO_index word_id [const restrict static 1]
+)
+{
+   ZoO_index current_max_score;
+   size_t i;
+   int success;
+
+   current_max_score = ZoO_INDEX_MAX;
+
+   success = -1;
+
+   for (i = 0; i < sequence_length; ++i)
+   {
+      if
+      (
+         (k->words[sequence[i]].occurrences <= current_max_score)
+         /* Otherwise we might just have learned it, or it must not be used. */
+         && (k->words[sequence[i]].occurrences > 1)
+      )
+      {
+         current_max_score = k->words[sequence[i]].occurrences;
+         *word_id = sequence[i];
+         success = 0;
+      }
+   }
+
+   return success;
+}
diff --git a/src/knowledge/knowledge.h b/src/knowledge/knowledge.h
index e97d84e..876dbe4 100644
--- a/src/knowledge/knowledge.h
+++ b/src/knowledge/knowledge.h
@@ -4,20 +4,20 @@
 #include "../core/char_types.h"
 #include "../core/index_types.h"
 
-#include "../pipe/pipe_types.h"
+#include "../error/error.h"
 
 #include "knowledge_types.h"
 
 int ZoO_knowledge_lock_access
 (
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 void ZoO_knowledge_unlock_access
 (
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 int ZoO_knowledge_initialize (struct ZoO_knowledge k [const restrict static 1]);
@@ -40,7 +40,7 @@ int ZoO_knowledge_learn_word
    const ZoO_char word [const restrict static 1],
    const size_t word_length,
    ZoO_index result [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 int ZoO_knowledge_learn_sequence
@@ -49,7 +49,7 @@ int ZoO_knowledge_learn_sequence
    const ZoO_index sequence [const restrict static 1],
    const size_t sequence_length,
    const ZoO_index markov_order,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 int ZoO_knowledge_learn_markov_sequence
@@ -58,7 +58,7 @@ int ZoO_knowledge_learn_markov_sequence
    const ZoO_index sequence [const restrict static 1],
    const ZoO_index markov_order, /* Pre (> markov_order 1) */
    ZoO_index sequence_id [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 void ZoO_knowledge_get_word
@@ -95,6 +95,14 @@ int ZoO_knowledge_find_sequence
    ZoO_index sequence_id [const restrict static 1]
 );
 
+int ZoO_knowledge_rarest_word
+(
+   const struct ZoO_knowledge k [const static 1],
+   const ZoO_index sequence [const restrict static 1],
+   const size_t sequence_length,
+   ZoO_index word_id [const restrict static 1]
+);
+
 int ZoO_knowledge_find_markov_sequence
 (
    const ZoO_index sequence_id,
@@ -131,7 +139,7 @@ int ZoO_knowledge_copy_random_swt_sequence
    ZoO_index sequence [const restrict static 1],
    const ZoO_index word_id,
    const ZoO_index markov_order,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 int ZoO_knowledge_strengthen_swt
@@ -140,7 +148,7 @@ int ZoO_knowledge_strengthen_swt
    const ZoO_index sequence_id,
    const ZoO_index word_id,
    const ZoO_index target_id,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 int ZoO_knowledge_strengthen_tws
@@ -149,7 +157,7 @@ int ZoO_knowledge_strengthen_tws
    const ZoO_index target_id,
    const ZoO_index word_id,
    const ZoO_index sequence_id,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 /*
@@ -162,7 +170,7 @@ int ZoO_knowledge_weaken_swt
    const ZoO_index sequence_id,
    const ZoO_index word_id,
    const ZoO_index target_id,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 int ZoO_knowledge_weaken_tws
@@ -171,7 +179,7 @@ int ZoO_knowledge_weaken_tws
    const ZoO_index target_id,
    const ZoO_index word_id,
    const ZoO_index sequence_id,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 */
 #endif
diff --git a/src/knowledge/knowledge_finalize.c b/src/knowledge/knowledge_finalize.c
index 6c249f0..37548d4 100644
--- a/src/knowledge/knowledge_finalize.c
+++ b/src/knowledge/knowledge_finalize.c
@@ -2,7 +2,6 @@
 
 #include "knowledge.h"
 
-
 static void knowledge_sequence_data_finalize
 (
    struct ZoO_knowledge_sequence_data sd [const restrict static 1]
diff --git a/src/knowledge/knowledge_get_random_sequence.c b/src/knowledge/knowledge_get_random_sequence.c
index 9055d31..92800a4 100644
--- a/src/knowledge/knowledge_get_random_sequence.c
+++ b/src/knowledge/knowledge_get_random_sequence.c
@@ -2,9 +2,10 @@
 
 #include "../core/char.h"
 #include "../core/index.h"
+
 #include "../sequence/sequence.h"
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "knowledge.h"
 
@@ -52,7 +53,7 @@ int ZoO_knowledge_copy_random_swt_sequence
    ZoO_index sequence [const restrict static 1],
    const ZoO_index word_id,
    const ZoO_index markov_order,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index sequence_id;
diff --git a/src/knowledge/knowledge_get_random_target.c b/src/knowledge/knowledge_get_random_target.c
index d9bf8a9..99fbc9b 100644
--- a/src/knowledge/knowledge_get_random_target.c
+++ b/src/knowledge/knowledge_get_random_target.c
@@ -2,9 +2,10 @@
 
 #include "../core/char.h"
 #include "../core/index.h"
-#include "../sequence/sequence.h"
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
+
+#include "../sequence/sequence.h"
 
 #include "knowledge.h"
 
diff --git a/src/knowledge/knowledge_learn_markov_sequence.c b/src/knowledge/knowledge_learn_markov_sequence.c
index 35cc123..54357c0 100644
--- a/src/knowledge/knowledge_learn_markov_sequence.c
+++ b/src/knowledge/knowledge_learn_markov_sequence.c
@@ -4,7 +4,7 @@
 
 #include "../sequence/sequence.h"
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "knowledge.h"
 
@@ -40,12 +40,12 @@ static void set_nth_sequence
 static int reallocate_sequences_list
 (
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index ** new_sequences;
 
-   if ((SIZE_MAX / sizeof(ZoO_index *)) > (size_t) k->sequences_length)
+   if ((SIZE_MAX / sizeof(ZoO_index *)) < (size_t) k->sequences_length)
    {
       ZoO_S_ERROR
       (
@@ -83,12 +83,12 @@ static int reallocate_sequences_list
 static int reallocate_sequences_sorted_list
 (
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index * new_sequences_sorted;
 
-   if ((SIZE_MAX / sizeof(ZoO_index)) > (size_t) k->sequences_length)
+   if ((SIZE_MAX / sizeof(ZoO_index)) < (size_t) k->sequences_length)
    {
       ZoO_S_ERROR
       (
@@ -104,7 +104,7 @@ static int reallocate_sequences_sorted_list
       (ZoO_index *) realloc
       (
          (void *) k->sequences_sorted,
-         ((size_t) k->sequences_length) * sizeof(ZoO_index)
+         (((size_t) k->sequences_length) * sizeof(ZoO_index))
       );
 
    if (new_sequences_sorted == (ZoO_index *) NULL)
@@ -144,7 +144,7 @@ static ZoO_index * copy_sequence
 (
    const ZoO_index base [const restrict static 1],
    const ZoO_index destination_length,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index i, diff;
@@ -189,7 +189,7 @@ static int add_sequence
    const ZoO_index markov_order, /* Pre (> markov_order 1) */
    const ZoO_index sequence_id,
    const ZoO_index sorted_sequence_id,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index * stored_sequence;
@@ -213,6 +213,30 @@ static int add_sequence
       return -1;
    }
 
+   if (ZoO_DEBUG_KNOWLEDGE_LEARN_SEQUENCE)
+   {
+      ZoO_index i;
+
+      ZoO_S_DEBUG
+      (
+         io,
+         ZoO_DEBUG_KNOWLEDGE_LEARN_SEQUENCE,
+         "Learning new sequence."
+      );
+
+      for (i = 0; i < (markov_order - 1); ++i)
+      {
+         ZoO_DEBUG
+         (
+            io,
+            ZoO_DEBUG_KNOWLEDGE_LEARN_SEQUENCE,
+            "markov_sequence[%u]: %u",
+            i,
+            stored_sequence[i]
+         );
+      }
+   }
+
    k->sequences_length += 1;
 
    if (reallocate_sequences_list(k, io) < 0)
@@ -271,16 +295,15 @@ int ZoO_knowledge_find_sequence
    current_min = 0;
    current_max -= 1;
 
-   for (;;)
+   while (current_min <= current_max)
    {
       i = (current_min + ((current_max - current_min) / 2));
 
       cmp =
          ZoO_sequence_cmp
          (
-            k->sequences[k->sequences_sorted[i]],
-            markov_sequence_length,
             sequence,
+            k->sequences[k->sequences_sorted[i]],
             markov_sequence_length
          );
 
@@ -297,9 +320,9 @@ int ZoO_knowledge_find_sequence
       }
       else if (cmp < 0)
       {
-         if ((current_min > current_max) || (i == 0))
+         if ((current_min >= current_max) || (i == 0))
          {
-            *sequence_id = i;
+            *sequence_id = current_min;
 
             return -1;
          }
@@ -313,6 +336,10 @@ int ZoO_knowledge_find_sequence
          return 0;
       }
    }
+
+   *sequence_id = current_min;
+
+   return -1;
 }
 
 /******************************************************************************/
@@ -325,11 +352,35 @@ int ZoO_knowledge_learn_markov_sequence
    const ZoO_index sequence [const restrict static 1],
    const ZoO_index markov_order, /* Pre (> markov_order 1) */
    ZoO_index sequence_id [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index sorted_id;
 
+   if (ZoO_DEBUG_KNOWLEDGE_LEARN_SEQUENCE)
+   {
+      ZoO_index i;
+
+      ZoO_S_DEBUG
+      (
+         io,
+         ZoO_DEBUG_KNOWLEDGE_LEARN_SEQUENCE,
+         "Studying markov sequence..."
+      );
+
+      for (i = 0; i < (markov_order - 1); ++i)
+      {
+         ZoO_DEBUG
+         (
+            io,
+            ZoO_DEBUG_KNOWLEDGE_LEARN_SEQUENCE,
+            "markov_sequence[%u]: %u",
+            i,
+            sequence[i]
+         );
+      }
+   }
+
    if
    (
       ZoO_knowledge_find_sequence
@@ -341,6 +392,14 @@ int ZoO_knowledge_learn_markov_sequence
       ) == 0
    )
    {
+      ZoO_DEBUG
+      (
+         io,
+         ZoO_DEBUG_KNOWLEDGE_LEARN_SEQUENCE,
+         "Markov sequence is known. ID: %u",
+         *sequence_id
+      );
+
       return 0;
    }
 
diff --git a/src/knowledge/knowledge_learn_sequence.c b/src/knowledge/knowledge_learn_sequence.c
index 6a666bd..b127bfb 100644
--- a/src/knowledge/knowledge_learn_sequence.c
+++ b/src/knowledge/knowledge_learn_sequence.c
@@ -4,7 +4,7 @@
 
 #include "../sequence/sequence.h"
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "knowledge.h"
 
@@ -26,8 +26,6 @@ static void parse_swt_sequence
 
    for (j = 0; j < buffer_length; ++j)
    {
-      index_offset = (buffer_length - j);
-
       if (index >= index_offset)
       {
          buffer[j] = sequence[index - index_offset];
@@ -36,6 +34,8 @@ static void parse_swt_sequence
       {
          buffer[j] = ZoO_START_OF_SEQUENCE_ID;
       }
+
+      --index_offset;
    }
 }
 
@@ -48,7 +48,7 @@ static int add_swt_sequence
    const ZoO_index markov_order,
    ZoO_index buffer [const restrict static 1],
    const ZoO_index buffer_length,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index sequence_id;
@@ -64,7 +64,7 @@ static int add_swt_sequence
          (buffer_length + 1),
          &sequence_id,
          io
-      )
+      ) < 0
    )
    {
       return -1;
@@ -110,15 +110,14 @@ static void parse_tws_sequence
 {
    size_t j;
    size_t index_offset;
-   const size_t remaining_items = (sequence_length - index);
 
    for (j = 0; j < buffer_length; ++j)
    {
-      index_offset = (j + 1);
+      index_offset = (j + 1) + index;
 
-      if (remaining_items > index_offset)
+      if (sequence_length > index_offset)
       {
-         buffer[j] = sequence[index + index_offset];
+         buffer[j] = sequence[index_offset];
       }
       else
       {
@@ -136,7 +135,7 @@ static int add_tws_sequence
    const ZoO_index markov_order,
    ZoO_index buffer [const restrict static 1],
    const ZoO_index buffer_length,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index sequence_id;
@@ -152,7 +151,7 @@ static int add_tws_sequence
          (buffer_length + 1),
          &sequence_id,
          io
-      )
+      ) < 0
    )
    {
       return -1;
@@ -193,7 +192,7 @@ int ZoO_knowledge_learn_sequence
    const ZoO_index sequence [const restrict static 1],
    const size_t sequence_length,
    const ZoO_index markov_order,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index * buffer;
@@ -220,30 +219,43 @@ int ZoO_knowledge_learn_sequence
 
    for (i = 0; i < sequence_length; ++i)
    {
-      /* TODO: handle failure. */
-      add_tws_sequence
+      if
       (
-         k,
-         sequence,
-         i,
-         sequence_length,
-         markov_order,
-         buffer,
-         buffer_length,
-         io
-      );
+         add_swt_sequence
+         (
+            k,
+            sequence,
+            i,
+            sequence_length,
+            markov_order,
+            buffer,
+            buffer_length,
+            io
+         ) < 0
+      )
+      {
+         return -1;
+      }
 
-      add_swt_sequence
+      /* TODO: handle failure. */
+      if
       (
-         k,
-         sequence,
-         i,
-         sequence_length,
-         markov_order,
-         buffer,
-         buffer_length,
-         io
-      );
+         add_tws_sequence
+         (
+            k,
+            sequence,
+            i,
+            sequence_length,
+            markov_order,
+            buffer,
+            buffer_length,
+            io
+         ) < 0
+      )
+      {
+         return -1;
+      }
+
 
       k->words[sequence[i]].occurrences += 1;
    }
diff --git a/src/knowledge/knowledge_learn_word.c b/src/knowledge/knowledge_learn_word.c
index 8430bc0..605af8e 100644
--- a/src/knowledge/knowledge_learn_word.c
+++ b/src/knowledge/knowledge_learn_word.c
@@ -2,7 +2,7 @@
 #include <string.h>
 #include <stdint.h> /* defines SIZE_MAX */
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "knowledge.h"
 
@@ -40,7 +40,7 @@ static ZoO_char * copy_word
 (
    const ZoO_char original [const restrict static 1],
    const ZoO_index original_length,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_char * result;
@@ -67,13 +67,13 @@ static ZoO_char * copy_word
       (((size_t) original_length) * sizeof(ZoO_char))
    );
 
-   return 0;
+   return result;
 }
 
 static int reallocate_words_list
 (
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    struct ZoO_knowledge_word * new_words;
@@ -81,7 +81,7 @@ static int reallocate_words_list
    if
    (
       (SIZE_MAX / sizeof(struct ZoO_knowledge_word))
-      > (size_t) k->words_length
+      < (size_t) k->words_length
    )
    {
       ZoO_S_ERROR
@@ -120,7 +120,7 @@ static int reallocate_words_list
 static int reallocate_words_sorted_list
 (
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index * new_words_sorted;
@@ -130,7 +130,7 @@ static int reallocate_words_sorted_list
     * whose size is bigger than a ZoO_index.
     * */
    /*
-   if ((SIZE_MAX / sizeof(ZoO_index)) > k->words_length)
+   if ((SIZE_MAX / sizeof(ZoO_index)) < k->words_length)
    {
       ZoO_S_ERROR
       (
@@ -197,7 +197,7 @@ static int add_word
    const ZoO_index word_length,
    const ZoO_index word_id,
    const ZoO_index sorted_word_id,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_char * stored_word;
@@ -244,7 +244,7 @@ static int add_word
 
    set_nth_word(k, sorted_word_id, word_id);
 
-   return -1;
+   return 0;
 }
 
 /******************************************************************************/
@@ -257,7 +257,7 @@ int ZoO_knowledge_learn_word
    const ZoO_char word [const restrict static 1],
    const size_t word_length,
    ZoO_index word_id [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index sorted_id;
@@ -280,11 +280,30 @@ int ZoO_knowledge_learn_word
       ) == 0
    )
    {
+      ZoO_DEBUG
+      (
+         io,
+         ZoO_DEBUG_KNOWLEDGE_LEARN_WORD,
+         "Word of size %u is already known (id: %u).",
+         (ZoO_index) word_length,
+         *word_id
+      );
+
       return 0;
    }
 
    sorted_id = *word_id;
    *word_id = k->words_length;
 
+   ZoO_DEBUG
+   (
+      io,
+      ZoO_DEBUG_KNOWLEDGE_LEARN_WORD,
+      "Learning new word of size %u (id: %u, sorted_id: %u).",
+      (ZoO_index) word_length,
+      *word_id,
+      sorted_id
+   );
+
    return add_word(k, word, (ZoO_index) word_length, *word_id, sorted_id, io);
 }
diff --git a/src/knowledge/knowledge_search.c b/src/knowledge/knowledge_search.c
index cc1934e..1163f61 100644
--- a/src/knowledge/knowledge_search.c
+++ b/src/knowledge/knowledge_search.c
@@ -4,7 +4,7 @@
 #include "../core/index.h"
 #include "../sequence/sequence.h"
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "knowledge.h"
 
@@ -36,11 +36,18 @@ int ZoO_knowledge_find_word_id
    current_min = 0;
    current_max -= 1;
 
-   for (;;)
+   while (current_min <= current_max)
    {
       i = (current_min + ((current_max - current_min) / 2));
 
-      cmp = ZoO_word_cmp(word, word_length, k->words[k->words_sorted[i]].word);
+      cmp =
+         ZoO_word_cmp
+         (
+            word,
+            word_length,
+            k->words[k->words_sorted[i]].word,
+            k->words[k->words_sorted[i]].word_length
+         );
 
       if (cmp > 0)
       {
@@ -55,7 +62,7 @@ int ZoO_knowledge_find_word_id
       }
       else if (cmp < 0)
       {
-         if ((current_min > current_max) || (i == 0))
+         if ((current_min >= current_max) || (i == 0))
          {
             *result = current_min;
 
@@ -71,6 +78,10 @@ int ZoO_knowledge_find_word_id
          return 0;
       }
    }
+
+   *result = current_min;
+
+   return -1;
 }
 
 int ZoO_knowledge_find_markov_sequence
@@ -94,7 +105,7 @@ int ZoO_knowledge_find_markov_sequence
    current_min = 0;
    current_max = (sc->sequences_ref_length - 1);
 
-   for (;;)
+   while (current_min <= current_max)
    {
       i = (current_min + ((current_max - current_min) / 2));
 
@@ -118,7 +129,7 @@ int ZoO_knowledge_find_markov_sequence
       }
       else if (cmp < 0)
       {
-         if ((current_min > current_max) || (i == 0))
+         if ((current_min >= current_max) || (i == 0))
          {
             *result = current_min;
 
@@ -134,6 +145,10 @@ int ZoO_knowledge_find_markov_sequence
          return 0;
       }
    }
+
+   *result = current_min;
+
+   return -1;
 }
 
 int ZoO_knowledge_find_sequence_target
@@ -157,7 +172,7 @@ int ZoO_knowledge_find_sequence_target
    current_min = 0;
    current_max = (sd->targets_length - 1);
 
-   for (;;)
+   while (current_min <= current_max)
    {
       i = (current_min + ((current_max - current_min) / 2));
 
@@ -176,7 +191,7 @@ int ZoO_knowledge_find_sequence_target
       }
       else if (cmp < 0)
       {
-         if ((current_min > current_max) || (i == 0))
+         if ((current_min >= current_max) || (i == 0))
          {
             *result = current_min;
 
@@ -192,4 +207,8 @@ int ZoO_knowledge_find_sequence_target
          return 0;
       }
    }
+
+   *result = current_min;
+
+   return -1;
 }
diff --git a/src/knowledge/knowledge_swt_tws_modifications.c b/src/knowledge/knowledge_swt_tws_modifications.c
index 40e2e3b..1a8048d 100644
--- a/src/knowledge/knowledge_swt_tws_modifications.c
+++ b/src/knowledge/knowledge_swt_tws_modifications.c
@@ -2,7 +2,7 @@
 
 #include "../core/index.h"
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "knowledge.h"
 
@@ -12,7 +12,7 @@ static int add_target
    const ZoO_index target_id,
    const ZoO_index s_index,
    const ZoO_index t_index,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    struct ZoO_knowledge_target * new_p;
@@ -68,7 +68,7 @@ static int add_sequence
    struct ZoO_knowledge_sequence_collection sc [const restrict static 1],
    const ZoO_index sequence_id,
    ZoO_index s_index [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    struct ZoO_knowledge_sequence_data * new_p;
@@ -149,7 +149,7 @@ static int add_sequence
    sc->sequences_ref[*s_index].targets = (struct ZoO_knowledge_target *) NULL;
    sc->sequences_ref[*s_index].targets_length = 0;
 
-   return -1;
+   return 0;
 }
 
 int ZoO_knowledge_strengthen_swt
@@ -158,7 +158,7 @@ int ZoO_knowledge_strengthen_swt
    const ZoO_index sequence_id,
    const ZoO_index word_id,
    const ZoO_index target_id,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index s_index, t_index;
@@ -248,7 +248,7 @@ int ZoO_knowledge_strengthen_tws
    const ZoO_index target_id,
    const ZoO_index word_id,
    const ZoO_index sequence_id,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index s_index, t_index;
@@ -278,7 +278,6 @@ int ZoO_knowledge_strengthen_tws
       }
    }
 
-
    if
    (
       ZoO_knowledge_find_sequence_target
@@ -330,5 +329,5 @@ int ZoO_knowledge_strengthen_tws
    k->words[word_id].tws.sequences_ref[s_index].occurrences += 1;
    k->words[word_id].tws.sequences_ref[s_index].targets[t_index].occurrences += 1;
 
-   return -1;
+   return 0;
 }
diff --git a/src/pervasive.h b/src/pervasive.h
index 6677c7e..d7b213f 100644
--- a/src/pervasive.h
+++ b/src/pervasive.h
@@ -14,6 +14,24 @@
    #define ZoO_DEBUG_ALL 0
 #endif
 
+#define ZoO_DEBUG_KNOWLEDGE (0 | ZoO_DEBUG_ALL)
+#define ZoO_DEBUG_KNOWLEDGE_LEARN_SEQUENCE \
+   (ZoO_DEBUG_KNOWLEDGE & (0 | ZoO_DEBUG_ALL))
+#define ZoO_DEBUG_KNOWLEDGE_LEARN_WORD \
+   (ZoO_DEBUG_KNOWLEDGE & (0 | ZoO_DEBUG_ALL))
+
+#define ZoO_DEBUG_SEQUENCE (0 | ZoO_DEBUG_ALL)
+#define ZoO_DEBUG_SEQUENCE_FROM_STRING \
+   (ZoO_DEBUG_SEQUENCE & (0 | ZoO_DEBUG_ALL))
+
+#define ZoO_DEBUG_SEQUENCE_CREATION \
+   (ZoO_DEBUG_SEQUENCE & (0 | ZoO_DEBUG_ALL))
+
+#define ZoO_DEBUG_SEQUENCE_CREATION_INIT \
+   (ZoO_DEBUG_SEQUENCE_CREATION & (0 | ZoO_DEBUG_ALL))
+
+#define ZoO_DEBUG_CORE (0 | ZoO_DEBUG_ALL)
+
 #define ZoO__TO_STRING(x) #x
 #define ZoO_TO_STRING(x) ZoO__TO_STRING(x)
 #define ZoO_ISOLATE(a) do {a} while (0)
diff --git a/src/pipe/pipe_types.h b/src/pipe/pipe_types.h
deleted file mode 100644
index 91cf0c3..0000000
--- a/src/pipe/pipe_types.h
+++ /dev/null
@@ -1,21 +0,0 @@
-#ifndef _ZoO_PIPE_PIPE_TYPES_H_
-#define _ZoO_PIPE_PIPE_TYPES_H_
-
-#define ZoO_PIPE_NAME_LENGTH 255
-
-#include <stdio.h>
-
-struct ZoO_pipe
-{
-   FILE * out;
-   FILE * in;
-};
-
-struct ZoO_pipe_names
-{
-   char request_pipe[ZoO_PIPE_NAME_LENGTH];
-   char reply_pipe[ZoO_PIPE_NAME_LENGTH];
-};
-//   const struct ZoO_pipe io [const restrict static 1]
-
-#endif
diff --git a/src/sequence/sequence.c b/src/sequence/sequence.c
index f3c3b46..78a5aad 100644
--- a/src/sequence/sequence.c
+++ b/src/sequence/sequence.c
@@ -5,74 +5,6 @@
 
 #include "sequence.h"
 
-/*
- * Bypass rendundant ZoO_START_OF_SEQUENCE_ID at the start of a sequence.
- */
-/*@
-   requires
-   (
-      \valid(sequence+ (0 .. sequence_length))
-      || (sequence_length == 0)
-   );
-   requires \separated(sequence, sequence_offset);
-
-   assigns (*sequence_offset);
-
-   ensures (*sequence_offset < sequence_length);
-
-   ensures
-   (
-      (*sequence_offset == 0)
-      || (sequence[0 .. *sequence_offset] == ZoO_START_OF_SEQUENCE_ID)
-   );
-
-   ensures
-   (
-      (*sequence_offset == sequence_length)
-      || (sequence[*sequence_offset + 1] != ZoO_START_OF_SEQUENCE_ID)
-   );
-
-@*/
-static void bypass_redundant_sos
-(
-   const ZoO_index sequence [const restrict],
-   const size_t sequence_length,
-   size_t sequence_offset [const restrict static 1]
-)
-{
-   ZoO_index i;
-
-   *sequence_offset = 0;
-
-   /*@
-      loop invariant 0 <= i <= sequence_length;
-      loop invariant (*sequence_offset <= i);
-      loop invariant
-      (
-         (*sequence_offset == 0)
-         || (sequence[*sequence_offset] == ZoO_START_OF_SEQUENCE_ID)
-      );
-      loop invariant
-         (
-            (i == 0) || (sequence[0 .. (i - 1)] == ZoO_START_OF_SEQUENCE_ID)
-         );
-      loop assigns i, *sequence_offset;
-      loop variant (sequence_length - i);
-   @*/
-   for (i = 0; i < sequence_length; ++i)
-   {
-      if (sequence[i] != ZoO_START_OF_SEQUENCE_ID)
-      {
-         return;
-      }
-      else if (sequence[i] == ZoO_START_OF_SEQUENCE_ID)
-      {
-         *sequence_offset = i;
-      }
-   }
-}
-
-
 /* See "sequence.h" */
 /*@
    requires
@@ -91,80 +23,28 @@ static void bypass_redundant_sos
 @*/
 int ZoO_sequence_cmp
 (
-   const ZoO_index sequence_a [const],
-   size_t sequence_a_length,
-   const ZoO_index sequence_b [const],
-   size_t sequence_b_length
+   const ZoO_index sequence_a [const restrict static 1],
+   const ZoO_index sequence_b [const restrict static 1],
+   const ZoO_index length
 )
 {
-   size_t min_length, a, b;
-   size_t a_offset, b_offset;
-   size_t i;
-   /*@ ghost size_t actual_a_length, actual_b_length; @*/
-
-   bypass_redundant_sos(sequence_a, sequence_a_length, &a_offset);
-   bypass_redundant_sos(sequence_b, sequence_b_length, &b_offset);
+   ZoO_index i, a, b;
 
-   /*@ ghost actual_a_length = sequence_a_length; @*/
-   /*@ ghost actual_b_length = sequence_b_length; @*/
-
-   /*@ assert (a_offset <= sequence_a_length); @*/
-   sequence_a_length -= a_offset;
-   /*@ assert (b_offset <= sequence_b_length); @*/
-   sequence_b_length -= b_offset;
-
-   if (sequence_a_length < sequence_b_length)
-   {
-      min_length = sequence_a_length;
-   }
-   else
+   for (i = 0; i < length; ++i)
    {
-      min_length = sequence_b_length;
-   }
-
-   /*@ assert (min_length <= sequence_a_length); @*/
-   /*@ assert (min_length <= sequence_b_length); @*/
-
-   /*@ assert (min_length + a_offset <= actual_a_length); @*/
-   /*@ assert (min_length + b_offset <= actual_b_length); @*/
-
-   /*@
-      loop invariant 0 <= i <= min_length;
-      loop assigns i;
-      loop variant (min_length - i);
-   @*/
-   for (i = 0; i < min_length; ++i)
-   {
-      /*@ assert ((i + a_offset) < actual_a_length); @*/
-      a = sequence_a[i + a_offset];
-      /*@ assert ((i + b_offset) < actual_b_length); @*/
-      b = sequence_b[i + b_offset];
+      a = sequence_a[i];
+      b = sequence_b[i];
 
       if (a < b)
       {
          return -1;
       }
-      else if (b > a)
+      else if (a > b)
       {
          return 1;
       }
-      else if ((a == ZoO_END_OF_SEQUENCE_ID) && (b == ZoO_END_OF_SEQUENCE_ID))
-      {
-         return 0;
-      }
    }
 
-   if (sequence_a_length > sequence_b_length)
-   {
-      return 1;
-   }
-   else if (sequence_a_length < sequence_b_length)
-   {
-      return -1;
-   }
-   else
-   {
-      return 0;
-   }
+   return 0;
 }
 
diff --git a/src/sequence/sequence.h b/src/sequence/sequence.h
index 129c457..9239336 100644
--- a/src/sequence/sequence.h
+++ b/src/sequence/sequence.h
@@ -7,7 +7,7 @@
 #include "../core/char_types.h"
 #include "../core/index_types.h"
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "../knowledge/knowledge_types.h"
 
@@ -15,16 +15,32 @@
 
 /*@
    requires \valid(sequence);
-   requires \valid(*sequence);
+   requires (\block_length(sequence) >= 1);
    requires \valid(sequence_capacity);
+   requires (\block_length(sequence) >= 1);
    requires \valid(io);
 
    requires (((*sequence_capacity) * sizeof(ZoO_index)) <= SIZE_MAX);
    requires ((sequence_required_capacity * sizeof(ZoO_index)) <= SIZE_MAX);
 
-   requires \separated(sequence, *sequence, sequence_capacity, io);
+   requires
+      \separated
+      (
+         (sequence+ (0 .. \block_length(sequence))),
+         ((*sequence)+ (0 .. \block_length(*sequence))),
+         (sequence_capacity+ (0 ..\block_length(sequence_capacity))),
+         (io+ (0 ..\block_length(io)))
+      );
+
+   ensures
+      \separated
+      (
+         (sequence+ (0 .. \block_length(sequence))),
+         ((*sequence)+ (0 .. \block_length(*sequence))),
+         (sequence_capacity+ (0 ..\block_length(sequence_capacity))),
+         (io+ (0 ..\block_length(io)))
+      );
 
-   ensures \separated(sequence, *sequence, sequence_capacity, io);
    ensures (((*sequence_capacity) * sizeof(ZoO_index)) <= SIZE_MAX);
    ensures ((sequence_required_capacity * sizeof(ZoO_index)) <= SIZE_MAX);
    ensures \valid(sequence);
@@ -70,7 +86,7 @@ int ZoO_sequence_ensure_capacity
    ZoO_index * sequence [const restrict static 1],
    size_t sequence_capacity [const restrict static 1],
    const size_t sequence_required_capacity,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 int ZoO_sequence_from_undercase_string
@@ -81,7 +97,7 @@ int ZoO_sequence_from_undercase_string
    ZoO_index * sequence [const restrict static 1],
    size_t sequence_capacity [const restrict static 1],
    size_t sequence_length [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 /*
@@ -114,7 +130,7 @@ int ZoO_sequence_create_from
    ZoO_index * sequence [const restrict static 1],
    size_t sequence_capacity [const restrict static 1],
    size_t sequence_length [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 /*@
@@ -125,7 +141,15 @@ int ZoO_sequence_create_from
    requires \valid(io);
    requires (((*sequence_length) * sizeof(ZoO_index)) <= SIZE_MAX);
    requires (((*sequence_capacity) * sizeof(ZoO_index)) <= SIZE_MAX);
-   requires \separated(sequence, *sequence, sequence_capacity, sequence_length, io);
+   requires
+      \separated
+      (
+         (sequence+ (0 .. \block_length(sequence))),
+         ((*sequence)+ (0 .. \block_length(*sequence))),
+         (sequence_capacity+ (0 ..\block_length(sequence_capacity))),
+         (sequence_length+ (0 ..\block_length(sequence_length))),
+         (io+ (0 ..\block_length(io)))
+      );
 
    assigns (*sequence_length);
    assigns (*sequence[0]);
@@ -138,7 +162,15 @@ int ZoO_sequence_create_from
    ensures \valid(io);
    ensures (((*sequence_length) * sizeof(ZoO_index)) <= SIZE_MAX);
    ensures (((*sequence_capacity) * sizeof(ZoO_index)) <= SIZE_MAX);
-   ensures \separated(sequence, *sequence, sequence_capacity, sequence_length, io);
+   ensures
+      \separated
+      (
+         (sequence+ (0 .. \block_length(sequence))),
+         ((*sequence)+ (0 .. \block_length(*sequence))),
+         (sequence_capacity+ (0 ..\block_length(sequence_capacity))),
+         (sequence_length+ (0 ..\block_length(sequence_length))),
+         (io+ (0 ..\block_length(io)))
+      );
 
    ensures ((\result == 0) || (\result == -1));
 
@@ -157,7 +189,7 @@ int ZoO_sequence_create_from
    ensures ((\result == 0) ==> (*sequence_length > \old(*sequence_length)));
 
    ensures ((\result == -1) ==> ((*sequence_length) == \old(*sequence_length)));
-   ensures ((\result == -1) ==> ((*sequence[0]) == \old(*sequence[0])));
+   ensures ((\result == -1) ==> (((*sequence)[0]) == \old((*sequence)[0])));
    ensures
       (
          (\result == -1) ==>
@@ -178,7 +210,7 @@ int ZoO_sequence_append_left
    ZoO_index * sequence [const restrict static 1],
    size_t sequence_capacity [const restrict static 1],
    size_t sequence_length [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 /*@
@@ -189,10 +221,18 @@ int ZoO_sequence_append_left
    requires \valid(io);
    requires (((*sequence_length) * sizeof(ZoO_index)) <= SIZE_MAX);
    requires (((*sequence_capacity) * sizeof(ZoO_index)) <= SIZE_MAX);
-   requires \separated(sequence, *sequence, sequence_capacity, sequence_length, io);
+   requires
+      \separated
+      (
+         (sequence+ (0 .. \block_length(sequence))),
+         ((*sequence)+ (0 .. \block_length(*sequence))),
+         (sequence_capacity+ (0 ..\block_length(sequence_capacity))),
+         (sequence_length+ (0 ..\block_length(sequence_length))),
+         (io+ (0 ..\block_length(io)))
+      );
 
    assigns (*sequence_length);
-   assigns (*sequence[0]);
+   assigns ((*sequence)[0]);
    assigns (*sequence_capacity);
 
    ensures \valid(sequence);
@@ -202,7 +242,15 @@ int ZoO_sequence_append_left
    ensures \valid(io);
    ensures (((*sequence_length) * sizeof(ZoO_index)) <= SIZE_MAX);
    ensures (((*sequence_capacity) * sizeof(ZoO_index)) <= SIZE_MAX);
-   ensures \separated(sequence, *sequence, sequence_capacity, sequence_length, io);
+   ensures
+      \separated
+      (
+         (sequence+ (0 .. \block_length(sequence))),
+         ((*sequence)+ (0 .. \block_length(*sequence))),
+         (sequence_capacity+ (0 ..\block_length(sequence_capacity))),
+         (sequence_length+ (0 ..\block_length(sequence_length))),
+         (io+ (0 ..\block_length(io)))
+      );
 
    ensures ((\result == 0) || (\result == -1));
 
@@ -221,7 +269,7 @@ int ZoO_sequence_append_left
    ensures ((\result == 0) ==> (*sequence_length > \old(*sequence_length)));
 
    ensures ((\result == -1) ==> ((*sequence_length) == \old(*sequence_length)));
-   ensures ((\result == -1) ==> ((*sequence[0]) == \old(*sequence[0])));
+   ensures ((\result == -1) ==> (((*sequence)[0]) == \old((*sequence)[0])));
    ensures
       (
          (\result == -1) ==>
@@ -242,7 +290,7 @@ int ZoO_sequence_append_right
    const ZoO_index word_id,
    size_t sequence_capacity [const restrict static 1],
    size_t sequence_length [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 /*
@@ -265,9 +313,19 @@ int ZoO_sequence_append_right
 int ZoO_sequence_cmp
 (
    const ZoO_index sequence_a [const],
-   size_t sequence_a_length,
    const ZoO_index sequence_b [const],
-   size_t sequence_b_length
+   const ZoO_index length
+);
+
+int ZoO_sequence_to_undercase_string
+(
+   const ZoO_index sequence [const restrict static 1],
+   const size_t sequence_length,
+   struct ZoO_knowledge k [const restrict static 1],
+   ZoO_char * destination [const restrict static 1],
+   size_t destination_capacity [const restrict static 1],
+   size_t destination_length [const restrict static 1],
+   FILE io [const restrict static 1]
 );
 
 #endif
diff --git a/src/sequence/sequence_append.c b/src/sequence/sequence_append.c
index 604d251..81dfa99 100644
--- a/src/sequence/sequence_append.c
+++ b/src/sequence/sequence_append.c
@@ -5,7 +5,7 @@
 
 #include "../core/index.h"
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "sequence.h"
 
@@ -16,10 +16,14 @@
 /*@
    requires \valid(required_capacity);
    requires \valid(io);
-   requires \separated(required_capacity, io);
+   requires
+      \separated
+      (
+         (required_capacity+ (0 .. \block_length(required_capacity))),
+         (io+ (0 .. \block_length(io)))
+      );
 
    assigns \result;
-
    assigns (*required_capacity);
 
    ensures ((\result == 0) || (\result == -1));
@@ -27,7 +31,12 @@
    ensures \valid(required_capacity);
    ensures \valid(io);
 
-   ensures \separated(required_capacity, io);
+   ensures
+      \separated
+      (
+         (required_capacity+ (0 .. \block_length(required_capacity))),
+         (io+ (0 .. \block_length(io)))
+      );
 
    ensures
       (
@@ -51,7 +60,7 @@
 static int increment_required_capacity
 (
    size_t required_capacity [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    if
@@ -92,7 +101,7 @@ int ZoO_sequence_ensure_capacity
    ZoO_index * sequence [const restrict static 1],
    size_t sequence_capacity [const restrict static 1],
    const size_t sequence_required_capacity,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index * new_sequence;
@@ -146,7 +155,7 @@ int ZoO_sequence_append_left
    ZoO_index * sequence [const restrict static 1],
    size_t sequence_capacity [const restrict static 1],
    size_t sequence_length [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    if (increment_required_capacity(sequence_length, io) < 0)
@@ -171,17 +180,17 @@ int ZoO_sequence_append_left
       return -1;
    }
 
-   /*@ assert *sequence_length >= 0; @*/
+   /*@ assert (*sequence_length) >= 0; @*/
 
-   if (*sequence_length > 1)
+   if ((*sequence_length) > 1)
    {
       /*@ assert(((*sequence_length) * sizeof(ZoO_index)) <= SIZE_MAX); @*/
 
       #ifndef ZoO_RUNNING_FRAMA_C
       memmove
       (
-         (void *) (*sequence + 1),
-         (const void *) sequence,
+         (void *) ((*sequence) + 1),
+         (const void *) (*sequence),
          (((*sequence_length) - 1) * sizeof(ZoO_index))
       );
       #endif
@@ -198,7 +207,7 @@ int ZoO_sequence_append_right
    const ZoO_index word_id,
    size_t sequence_capacity [const restrict static 1],
    size_t sequence_length [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    if (increment_required_capacity(sequence_length, io) < 0)
@@ -206,7 +215,7 @@ int ZoO_sequence_append_right
       return -1;
    }
 
-   /*@ assert ((*sequence_length * sizeof(ZoO_index)) <= SIZE_MAX); @*/
+   /*@ assert (((*sequence_length) * sizeof(ZoO_index)) <= SIZE_MAX); @*/
 
    if
    (
@@ -224,9 +233,9 @@ int ZoO_sequence_append_right
       return -1;
    }
 
-   /*@ assert (*sequence_length >= 1); @*/
-   (*sequence)[*sequence_length - 1] = word_id;
-   /*@ assert (*sequence_length >= 1); @*/
+   /*@ assert ((*sequence_length) >= 1); @*/
+   (*sequence)[(*sequence_length) - 1] = word_id;
+   /*@ assert ((*sequence_length) >= 1); @*/
 
    return 0;
 }
diff --git a/src/sequence/sequence_creation.c b/src/sequence/sequence_creation.c
index 1f20262..9556693 100644
--- a/src/sequence/sequence_creation.c
+++ b/src/sequence/sequence_creation.c
@@ -5,7 +5,7 @@
 
 #include "../core/index.h"
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "../knowledge/knowledge.h"
 
@@ -40,7 +40,7 @@ static int extend_left
    size_t sequence_length [const restrict static 1],
    const ZoO_index markov_order,
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index sequence_id, word_id;
@@ -62,7 +62,8 @@ static int extend_left
    {
       (void) ZoO_knowledge_unlock_access(k, io);
 
-      /* TODO: Err message. */
+      ZoO_S_ERROR(io, "Could not find matching TWS sequence.");
+
       return -1;
    }
 
@@ -83,7 +84,7 @@ static int extend_left
    {
       (void) ZoO_knowledge_unlock_access(k, io);
 
-      /* TODO: Err message. */
+      ZoO_S_ERROR(io, "Could not find matching TWS target.");
 
       return -1;
    }
@@ -138,7 +139,7 @@ static int complete_left_part_of_sequence
    const ZoO_index markov_order,
    size_t credits [const restrict],
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    for (;;)
@@ -159,7 +160,7 @@ static int complete_left_part_of_sequence
          )
          {
             /* We are sure *sequence[0] is defined. */
-            if (*sequence[0] == ZoO_START_OF_SEQUENCE_ID)
+            if ((*sequence)[0] == ZoO_START_OF_SEQUENCE_ID)
             {
                /*
                 * We failed to add a word, but it was because none should have
@@ -176,7 +177,7 @@ static int complete_left_part_of_sequence
       else
       {
          /* No more credits available, the sequence will have to start here. */
-         *sequence[0] = ZoO_START_OF_SEQUENCE_ID;
+         (*sequence)[0] = ZoO_START_OF_SEQUENCE_ID;
 
          return 0;
       }
@@ -187,7 +188,7 @@ static int complete_left_part_of_sequence
       }
 
       /* We are sure *sequence[0] is defined. */
-      switch (*sequence[0])
+      switch ((*sequence)[0])
       {
          case ZoO_END_OF_SEQUENCE_ID:
             ZoO_S_WARNING
@@ -196,7 +197,7 @@ static int complete_left_part_of_sequence
                "END OF LINE was added at the left part of an sequence."
             );
 
-            *sequence[0] = ZoO_START_OF_SEQUENCE_ID;
+            (*sequence)[0] = ZoO_START_OF_SEQUENCE_ID;
             return 0;
 
          case ZoO_START_OF_SEQUENCE_ID:
@@ -237,7 +238,7 @@ static int extend_right
    size_t sequence_length [const restrict static 1],
    const ZoO_index markov_order,
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index sequence_id, word_id;
@@ -342,7 +343,7 @@ static int complete_right_part_of_sequence
    const ZoO_index markov_order,
    size_t credits [const restrict],
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    for (;;)
@@ -363,7 +364,7 @@ static int complete_right_part_of_sequence
          )
          {
             /* Safe: (> sequence_length 1) */
-            if (*sequence[(*sequence_length - 1)] == ZoO_END_OF_SEQUENCE_ID)
+            if ((*sequence)[(*sequence_length - 1)] == ZoO_END_OF_SEQUENCE_ID)
             {
                /*
                 * We failed to add a word, but it was because none should have
@@ -380,7 +381,7 @@ static int complete_right_part_of_sequence
       else
       {
          /* No more credits available, we end the sequence. */
-         *sequence[(*sequence_length - 1)] = ZoO_END_OF_SEQUENCE_ID;
+         (*sequence)[((*sequence_length) - 1)] = ZoO_END_OF_SEQUENCE_ID;
 
          return 0;
       }
@@ -391,7 +392,7 @@ static int complete_right_part_of_sequence
       }
 
       /* Safe: (> sequence_length 1) */
-      switch (*sequence[(*sequence_length - 1)])
+      switch ((*sequence)[((*sequence_length) - 1)])
       {
          case ZoO_START_OF_SEQUENCE_ID:
             ZoO_S_WARNING
@@ -400,7 +401,7 @@ static int complete_right_part_of_sequence
                "END OF LINE was added at the right part of an sequence."
             );
 
-            *sequence[(*sequence_length - 1)] = ZoO_END_OF_SEQUENCE_ID;
+            (*sequence)[((*sequence_length) - 1)] = ZoO_END_OF_SEQUENCE_ID;
             return 0;
 
          case ZoO_END_OF_SEQUENCE_ID:
@@ -438,7 +439,7 @@ static int initialize_sequence
    const ZoO_index initial_word,
    const ZoO_index markov_order,
    struct ZoO_knowledge k [const static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    sequence[(markov_order - 1)] = initial_word;
@@ -467,6 +468,23 @@ static int initialize_sequence
       return -1;
    }
 
+   if (ZoO_DEBUG_SEQUENCE_CREATION_INIT)
+   {
+      ZoO_index i;
+
+      for (i = 0; i < markov_order; ++i)
+      {
+         ZoO_DEBUG
+         (
+            io,
+            ZoO_DEBUG_SEQUENCE_CREATION_INIT,
+            "sequence[%u]: %u",
+            i,
+            sequence[i]
+         );
+      }
+   }
+
    (void) ZoO_knowledge_unlock_access(k, io);
 
    return 0;
@@ -486,9 +504,11 @@ int ZoO_sequence_create_from
    ZoO_index * sequence [const restrict static 1],
    size_t sequence_capacity [const restrict static 1],
    size_t sequence_length [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
+   size_t i;
+
    if
    (
       ZoO_sequence_ensure_capacity
@@ -517,6 +537,8 @@ int ZoO_sequence_create_from
       ) < 0
    )
    {
+      ZoO_S_ERROR(io, "Failed to create start of new sequence.");
+
       *sequence_length = 0;
 
       return -2;
@@ -538,6 +560,8 @@ int ZoO_sequence_create_from
       ) < 0
    )
    {
+      ZoO_S_ERROR(io, "Failed to create right part of sequence.");
+
       *sequence_length = 0;
 
       return -3;
@@ -557,6 +581,8 @@ int ZoO_sequence_create_from
       ) < 0
    )
    {
+      ZoO_S_ERROR(io, "Failed to create left part of sequence.");
+
       *sequence_length = 0;
 
       return -4;
diff --git a/src/sequence/sequence_from_string.c b/src/sequence/sequence_from_string.c
index 6acfdc2..e493bbc 100644
--- a/src/sequence/sequence_from_string.c
+++ b/src/sequence/sequence_from_string.c
@@ -6,7 +6,7 @@
 #include "../core/char.h"
 #include "../core/index.h"
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "../knowledge/knowledge.h"
 
@@ -25,17 +25,12 @@ static int add_word_to_sequence
    size_t sequence_capacity [const restrict static 1],
    size_t sequence_length [const restrict static 1],
    struct ZoO_knowledge k [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_index word_id;
    ZoO_char * stored_word;
 
-   if (word_length == 0)
-   {
-      return 0;
-   }
-
    (void) ZoO_knowledge_lock_access(k, io);
 
    if
@@ -105,11 +100,6 @@ static int find_word
       i += 1;
    }
 
-   if (i >= string_length)
-   {
-      return -1;
-   }
-
    *word_length = (i - *word_start);
 
    return 0;
@@ -128,7 +118,7 @@ int ZoO_sequence_from_undercase_string
    ZoO_index * sequence [const restrict static 1],
    size_t sequence_capacity [const restrict static 1],
    size_t sequence_length [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    size_t word_start, word_length;
@@ -136,9 +126,16 @@ int ZoO_sequence_from_undercase_string
 
    i = 0;
 
-   *sequence = (ZoO_index *) NULL;
    *sequence_length = 0;
 
+   ZoO_DEBUG
+   (
+      io,
+      ZoO_DEBUG_SEQUENCE_FROM_STRING,
+      "Converting string of size %lu to sequence.",
+      string_length
+   );
+
    if
    (
       ZoO_sequence_append_right
@@ -151,16 +148,34 @@ int ZoO_sequence_from_undercase_string
       ) < 0
    )
    {
+      *sequence_length = 0;
+
       return -1;
    }
 
+   ZoO_S_DEBUG
+   (
+      io,
+      ZoO_DEBUG_SEQUENCE_FROM_STRING,
+      "[SOS] added to sequence."
+   );
+
    while (i < string_length)
    {
-      if (find_word(string, i, string_length, &word_start, &word_length) < 0)
+      if (find_word(string, string_length, i, &word_start, &word_length) < 0)
       {
          break;
       }
 
+      ZoO_DEBUG
+      (
+         io,
+         ZoO_DEBUG_SEQUENCE_FROM_STRING,
+         "Word of size %lu found in string at index %lu.",
+         word_length,
+         word_start
+      );
+
       if
       (
          add_word_to_sequence
@@ -176,8 +191,6 @@ int ZoO_sequence_from_undercase_string
          ) < 0
       )
       {
-         free((void *) *sequence);
-         *sequence = (ZoO_index *) NULL;
          *sequence_length = 0;
 
          return -1;
@@ -198,9 +211,6 @@ int ZoO_sequence_from_undercase_string
       ) < 0
    )
    {
-      free((void *) *sequence);
-
-      *sequence = (ZoO_index *) NULL;
       *sequence_length = 0;
 
       return -1;
diff --git a/src/sequence/sequence_to_string.c b/src/sequence/sequence_to_string.c
index 96bd521..919ef0b 100644
--- a/src/sequence/sequence_to_string.c
+++ b/src/sequence/sequence_to_string.c
@@ -6,7 +6,7 @@
 #include "../core/char.h"
 #include "../core/index.h"
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "../knowledge/knowledge.h"
 
@@ -20,7 +20,7 @@ static int ensure_string_capacity
    ZoO_char * string [const restrict static 1],
    size_t string_capacity [const restrict static 1],
    const size_t string_required_capacity,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    ZoO_char * new_string;
@@ -61,10 +61,10 @@ static int increment_required_capacity
 (
    size_t current_capacity [const restrict static 1],
    const size_t increase_factor,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
-   if ((ZoO_INDEX_MAX - increase_factor) > *current_capacity)
+   if ((ZoO_INDEX_MAX - increase_factor) < *current_capacity)
    {
       ZoO_S_ERROR
       (
@@ -78,7 +78,7 @@ static int increment_required_capacity
 
    *current_capacity += increase_factor;
 
-   if ((SIZE_MAX / sizeof(ZoO_char)) > *current_capacity)
+   if ((SIZE_MAX / sizeof(ZoO_char)) < *current_capacity)
    {
       *current_capacity -= increase_factor;
 
@@ -102,13 +102,18 @@ static int add_word
    ZoO_char * destination [const restrict static 1],
    size_t destination_capacity [const restrict static 1],
    size_t destination_length [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
 	const ZoO_char * word;
 	ZoO_index word_size;
    size_t insertion_point;
 
+   if (word_id < ZoO_RESERVED_IDS_COUNT)
+   {
+      return 0;
+   }
+
 	(void) ZoO_knowledge_lock_access(k, io);
 	ZoO_knowledge_get_word(k, word_id, &word, &word_size);
 	(void) ZoO_knowledge_unlock_access(k, io);
@@ -155,15 +160,17 @@ int ZoO_sequence_to_undercase_string
 (
    const ZoO_index sequence [const restrict static 1],
    const size_t sequence_length,
-   ZoO_char * destination [const restrict static 1],
    struct ZoO_knowledge k [const restrict static 1],
+   ZoO_char * destination [const restrict static 1],
    size_t destination_capacity [const restrict static 1],
    size_t destination_length [const restrict static 1],
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    size_t i;
 
+   *destination_length = 0;
+
    for (i = 0; i < sequence_length; ++i)
    {
       if
diff --git a/src/server/CMakeLists.txt b/src/server/CMakeLists.txt
index ca476fb..3b64500 100644
--- a/src/server/CMakeLists.txt
+++ b/src/server/CMakeLists.txt
@@ -11,6 +11,7 @@ set(
    ${CMAKE_CURRENT_SOURCE_DIR}/server_worker.c
    ${CMAKE_CURRENT_SOURCE_DIR}/server_worker_handle_request.c
    ${CMAKE_CURRENT_SOURCE_DIR}/server_worker_receive.c
+   ${CMAKE_CURRENT_SOURCE_DIR}/server_worker_send.c
 )
 
 set(SRC_FILES ${SRC_FILES} PARENT_SCOPE)
diff --git a/src/server/server.c b/src/server/server.c
index 197faf6..edd1bd7 100644
--- a/src/server/server.c
+++ b/src/server/server.c
@@ -84,3 +84,4 @@ int ZoO_server_main
 
    return 0;
 }
+
diff --git a/src/server/server.h b/src/server/server.h
index 90103ed..b8c0bc8 100644
--- a/src/server/server.h
+++ b/src/server/server.h
@@ -55,4 +55,24 @@ int ZoO_server_worker_handle_request
    struct ZoO_server_worker worker [const restrict static 1]
 );
 
+int ZoO_server_worker_send_confirm_protocol_version
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+);
+
+int ZoO_server_worker_send_positive
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+);
+
+int ZoO_server_worker_send_negative
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+);
+
+int ZoO_server_worker_send_generated_reply
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+);
+
 #endif
diff --git a/src/server/server_initialize.c b/src/server/server_initialize.c
index 9213156..e0632a4 100644
--- a/src/server/server_initialize.c
+++ b/src/server/server_initialize.c
@@ -4,6 +4,8 @@
 
 #include "../parameters/parameters.h"
 
+#include "../knowledge/knowledge.h"
+
 #include "server.h"
 
 static int initialize_worker_collection
@@ -67,6 +69,7 @@ void initialize_thread_parameters
 {
    server->thread_params.thread_collection = &(server->workers);
    server->thread_params.server_params = params;
+   server->thread_params.knowledge = &(server->k);
    server->thread_params.socket = -1;
 }
 
@@ -81,6 +84,11 @@ int ZoO_server_initialize
       return -1;
    }
 
+   if (ZoO_knowledge_initialize(&(server->k)) < 0)
+   {
+      return -1;
+   }
+
    if
    (
       ZoO_server_socket_open
diff --git a/src/server/server_new_connection.c b/src/server/server_new_connection.c
index 5392de5..46b38fc 100644
--- a/src/server/server_new_connection.c
+++ b/src/server/server_new_connection.c
@@ -89,7 +89,7 @@ static int get_new_thread (struct ZoO_server server [const restrict static 1])
    new_threads =
       (struct ZoO_server_thread_data *) realloc
       (
-         &(server->workers.threads),
+         server->workers.threads,
          (
             sizeof(struct ZoO_server_thread_data)
             * ((size_t) server->workers.threads_capacity)
diff --git a/src/server/server_types.h b/src/server/server_types.h
index 1ba9f96..a6fb875 100644
--- a/src/server/server_types.h
+++ b/src/server/server_types.h
@@ -13,7 +13,7 @@
 
 #include "../parameters/parameters_types.h"
 
-#include "../pipe/pipe_types.h"
+#include "../error/error.h"
 
 #define ZoO_SERVER_MAX_RETRIES 10
 #define ZoO_SERVER_BUFFER_SIZE 0
@@ -66,10 +66,15 @@ struct ZoO_server_thread_parameters
 struct ZoO_server_worker
 {
    struct ZoO_server_thread_parameters params;
+   FILE * socket_as_file;
+
    char * buffer;
    size_t buffer_capacity;
    size_t buffer_length;
-   FILE * socket_as_file;
+
+   ZoO_index * sequence_buffer;
+   size_t sequence_buffer_capacity;
+   size_t sequence_buffer_length;
 };
 
 struct ZoO_server
@@ -77,6 +82,7 @@ struct ZoO_server
    struct ZoO_server_thread_collection workers;
    struct ZoO_server_socket socket;
    struct ZoO_server_thread_parameters thread_params;
+   struct ZoO_knowledge k;
 };
 
 #endif
diff --git a/src/server/server_worker.c b/src/server/server_worker.c
index bd3b5d1..c96f92e 100644
--- a/src/server/server_worker.c
+++ b/src/server/server_worker.c
@@ -23,6 +23,10 @@ static int initialize
    worker->buffer_capacity = 0;
    worker->buffer_length = 0;
 
+   worker->sequence_buffer = (ZoO_index *) NULL;
+   worker->sequence_buffer_capacity = 0;
+   worker->sequence_buffer_length = 0;
+
    worker->socket_as_file = fdopen(worker->params.socket, "w+");
 
    if (worker->socket_as_file == (FILE *) NULL)
diff --git a/src/server/server_worker_handle_request.c b/src/server/server_worker_handle_request.c
index 0c97091..a1450df 100644
--- a/src/server/server_worker_handle_request.c
+++ b/src/server/server_worker_handle_request.c
@@ -1,11 +1,423 @@
+#include "../pervasive.h"
+
+#include "../error/error.h"
+
+#include "../sequence/sequence.h"
+
+#include "../knowledge/knowledge.h"
+
+#include "../parameters/parameters.h"
+
+#include "../storage/storage.h"
+
 #include "server.h"
 
-int ZoO_server_worker_handle_request
+static int load_reply
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+)
+{
+   ZoO_index rarest_word_id;
+
+   if
+   (
+      ZoO_knowledge_lock_access
+      (
+         worker->params.knowledge,
+         worker->socket_as_file
+      ) < 0
+   )
+   {
+      return -1;
+   }
+
+   if
+   (
+      ZoO_knowledge_rarest_word
+      (
+         worker->params.knowledge,
+         worker->sequence_buffer,
+         worker->sequence_buffer_length,
+         &rarest_word_id
+      ) < 0
+   )
+   {
+      ZoO_S_ERROR(worker->socket_as_file, "Could not find rarest word.");
+
+      ZoO_knowledge_unlock_access
+      (
+         worker->params.knowledge,
+         worker->socket_as_file
+      );
+
+      return -1;
+   }
+
+   ZoO_knowledge_unlock_access
+   (
+      worker->params.knowledge,
+      worker->socket_as_file
+   );
+
+   ZoO_DEBUG
+   (
+      worker->socket_as_file,
+      1,
+      "Word selected as pillar: %u",
+      rarest_word_id
+   );
+
+   if
+   (
+      ZoO_sequence_create_from
+      (
+         rarest_word_id,
+         (size_t *) NULL,
+         worker->params.knowledge,
+         ZoO_parameters_get_markov_order(worker->params.server_params),
+			&(worker->sequence_buffer),
+			&(worker->sequence_buffer_capacity),
+			&(worker->sequence_buffer_length),
+			worker->socket_as_file
+      ) < 0
+   )
+   {
+      ZoO_S_ERROR(worker->socket_as_file, "Could not create reply from selected word.");
+
+      return -1;
+   }
+
+   if
+   (
+      ZoO_sequence_to_undercase_string
+      (
+	   	worker->sequence_buffer,
+	   	worker->sequence_buffer_length,
+         worker->params.knowledge,
+			&(worker->buffer),
+			&(worker->buffer_capacity),
+			&(worker->buffer_length),
+			worker->socket_as_file
+      ) < 0
+   )
+   {
+      ZoO_S_ERROR(worker->socket_as_file, "Could not convert reply sequence to string.");
+
+      return -1;
+   }
+
+   return 0;
+}
+
+static int handle_rpv
 (
    struct ZoO_server_worker worker [const restrict static 1]
 )
 {
    /* TODO */
 
+   return -1;
+}
+
+static int handle_rl
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+)
+{
+   if
+   (
+      ZoO_sequence_from_undercase_string
+		(
+			(const ZoO_char *) (worker->buffer + 4),
+			(worker->buffer_length - 5),
+			worker->params.knowledge,
+			&(worker->sequence_buffer),
+			&(worker->sequence_buffer_capacity),
+			&(worker->sequence_buffer_length),
+			worker->socket_as_file
+		) < 0
+   )
+   {
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   if
+   (
+      ZoO_knowledge_lock_access
+      (
+         worker->params.knowledge,
+         worker->socket_as_file
+      ) < 0
+   )
+   {
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   if
+   (
+      ZoO_knowledge_learn_sequence
+      (
+         worker->params.knowledge,
+         worker->sequence_buffer,
+         worker->sequence_buffer_length,
+         ZoO_parameters_get_markov_order(worker->params.server_params),
+         worker->socket_as_file
+      ) < 0
+   )
+   {
+      ZoO_knowledge_unlock_access
+      (
+         worker->params.knowledge,
+         worker->socket_as_file
+      );
+
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   ZoO_knowledge_unlock_access
+   (
+      worker->params.knowledge,
+      worker->socket_as_file
+   );
+
+   return ZoO_server_worker_send_positive(worker);
+}
+
+static int handle_rls
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+)
+{
+   if
+   (
+      ZoO_sequence_from_undercase_string
+		(
+			(const ZoO_char *) (worker->buffer + 5),
+			(worker->buffer_length - 6),
+			worker->params.knowledge,
+			&(worker->sequence_buffer),
+			&(worker->sequence_buffer_capacity),
+			&(worker->sequence_buffer_length),
+			worker->socket_as_file
+		) < 0
+   )
+   {
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   if
+   (
+      ZoO_knowledge_lock_access
+      (
+         worker->params.knowledge,
+         worker->socket_as_file
+      ) < 0
+   )
+   {
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   if
+   (
+      ZoO_knowledge_learn_sequence
+      (
+         worker->params.knowledge,
+         worker->sequence_buffer,
+         worker->sequence_buffer_length,
+         ZoO_parameters_get_markov_order(worker->params.server_params),
+         worker->socket_as_file
+      ) < 0
+   )
+   {
+      ZoO_knowledge_unlock_access
+      (
+         worker->params.knowledge,
+         worker->socket_as_file
+      );
+
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   ZoO_knowledge_unlock_access
+   (
+      worker->params.knowledge,
+      worker->socket_as_file
+   );
+
+   if
+   (
+      ZoO_storage_write_line
+      (
+         ZoO_parameters_get_storage_filename(worker->params.server_params),
+         (worker->buffer + 5),
+         (worker->buffer_length - 5), /* Keep the \n this time. */
+         worker->socket_as_file
+      ) < 0
+   )
+   {
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   return ZoO_server_worker_send_positive(worker);
+}
+
+static int handle_rlsr
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+)
+{
+   if
+   (
+      ZoO_sequence_from_undercase_string
+		(
+			(const ZoO_char *) (worker->buffer + 6),
+			(worker->buffer_length - 7),
+			worker->params.knowledge,
+			&(worker->sequence_buffer),
+			&(worker->sequence_buffer_capacity),
+			&(worker->sequence_buffer_length),
+			worker->socket_as_file
+		) < 0
+   )
+   {
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   if
+   (
+      ZoO_knowledge_lock_access
+      (
+         worker->params.knowledge,
+         worker->socket_as_file
+      ) < 0
+   )
+   {
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   if
+   (
+      ZoO_knowledge_learn_sequence
+      (
+         worker->params.knowledge,
+         worker->sequence_buffer,
+         worker->sequence_buffer_length,
+         ZoO_parameters_get_markov_order(worker->params.server_params),
+         worker->socket_as_file
+      ) < 0
+   )
+   {
+      ZoO_knowledge_unlock_access
+      (
+         worker->params.knowledge,
+         worker->socket_as_file
+      );
+
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   ZoO_knowledge_unlock_access
+   (
+      worker->params.knowledge,
+      worker->socket_as_file
+   );
+
+   if
+   (
+      ZoO_storage_write_line
+      (
+         ZoO_parameters_get_storage_filename(worker->params.server_params),
+         (worker->buffer + 6),
+         (worker->buffer_length - 6), /* Keep the \n this time. */
+         worker->socket_as_file
+      ) < 0
+   )
+   {
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   if (load_reply(worker) < 0)
+   {
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   if (ZoO_server_worker_send_generated_reply(worker) < 0)
+   {
+      return -1;
+   }
+
+   return ZoO_server_worker_send_positive(worker);
+}
+
+static int handle_rr
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+)
+{
+   if
+   (
+      ZoO_sequence_from_undercase_string
+		(
+			(const ZoO_char *) (worker->buffer + 4),
+			(worker->buffer_length - 5),
+			worker->params.knowledge,
+			&(worker->sequence_buffer),
+			&(worker->sequence_buffer_capacity),
+			&(worker->sequence_buffer_length),
+			worker->socket_as_file
+		) < 0
+   )
+   {
+      ZoO_S_DEBUG(worker->socket_as_file, 1, "?RR failed at string to sequence.");
+
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   if (load_reply(worker) < 0)
+   {
+      ZoO_S_DEBUG(worker->socket_as_file, 1, "?RR failed at load reply.");
+      return ZoO_server_worker_send_negative(worker);
+   }
+
+   if (ZoO_server_worker_send_generated_reply(worker) < 0)
+   {
+      return -1;
+   }
+
+   return ZoO_server_worker_send_positive(worker);
+}
+
+int ZoO_server_worker_handle_request
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+)
+{
+   if (ZoO_IS_PREFIX("?RPV ", worker->buffer))
+   {
+      return handle_rpv(worker);
+   }
+   else if (ZoO_IS_PREFIX("?RL ", worker->buffer))
+   {
+      return handle_rl(worker);
+   }
+   else if (ZoO_IS_PREFIX("?RLS ", worker->buffer))
+   {
+      return handle_rls(worker);
+   }
+   else if (ZoO_IS_PREFIX("?RLSR ", worker->buffer))
+   {
+      return handle_rlsr(worker);
+   }
+   else if (ZoO_IS_PREFIX("?RR ", worker->buffer))
+   {
+      return handle_rr(worker);
+   }
+   else
+   {
+      ZoO_S_ERROR(worker->socket_as_file, "Unsupported request received.");
+
+      return ZoO_server_worker_send_negative(worker);
+   }
+
    return 0;
 }
diff --git a/src/server/server_worker_receive.c b/src/server/server_worker_receive.c
index 4dc2fc7..10944a9 100644
--- a/src/server/server_worker_receive.c
+++ b/src/server/server_worker_receive.c
@@ -1,6 +1,5 @@
 #include "server.h"
 
-
 int ZoO_server_worker_receive
 (
    struct ZoO_server_worker worker [const restrict static 1]
diff --git a/src/server/server_worker_send.c b/src/server/server_worker_send.c
new file mode 100644
index 0000000..6ba6d67
--- /dev/null
+++ b/src/server/server_worker_send.c
@@ -0,0 +1,106 @@
+#include "../pervasive.h"
+
+#include "server.h"
+
+int ZoO_server_worker_send_confirm_protocol_version
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+)
+{
+   int err;
+
+   err = fprintf(worker->socket_as_file, "!CPV 1\n");
+
+   if (err <= 0)
+   {
+      /* TODO: error message? */
+
+      return -1;
+   }
+
+   return 0;
+}
+
+int ZoO_server_worker_send_positive
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+)
+{
+   int err;
+
+   err = fprintf(worker->socket_as_file, "!P\n");
+
+   if (err <= 0)
+   {
+      /* TODO: error message? */
+
+      return -1;
+   }
+
+   return 0;
+}
+
+int ZoO_server_worker_send_negative
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+)
+{
+   int err;
+
+   err = fprintf(worker->socket_as_file, "!N\n");
+
+   if (err <= 0)
+   {
+      /* TODO: error message? */
+
+      return -1;
+   }
+
+   return 0;
+}
+
+int ZoO_server_worker_send_generated_reply
+(
+   struct ZoO_server_worker worker [const restrict static 1]
+)
+{
+   int err;
+
+   /* TODO */
+   err = fputs
+   (
+      "!GR ",
+      worker->socket_as_file
+   );
+
+   if (err <= 0)
+   {
+      /* TODO: error message? */
+
+      return -1;
+   }
+
+   err =
+      fwrite
+      (
+         worker->buffer,
+         sizeof(ZoO_char),
+         worker->buffer_length,
+         worker->socket_as_file
+      );
+
+   err = fputs
+   (
+      "\n",
+      worker->socket_as_file
+   );
+
+   if (err <= 0)
+   {
+      /* TODO: error message? */
+
+      return -1;
+   }
+
+   return 0;
+}
diff --git a/src/storage/storage.c b/src/storage/storage.c
index 22c5c49..40185a3 100644
--- a/src/storage/storage.c
+++ b/src/storage/storage.c
@@ -6,7 +6,7 @@
 #include <stdint.h> /* defines SIZE_MAX */
 #include <stdio.h>
 
-#include "../pipe/pipe.h"
+#include "../error/error.h"
 
 #include "storage.h"
 
@@ -15,12 +15,17 @@ int ZoO_storage_write_line
    const char filename [const restrict static 1],
    char line [const restrict static 1],
    size_t const line_size,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 )
 {
    const int old_errno = errno;
    FILE * file;
 
+   if (filename == (const char *) NULL)
+   {
+      return 0;
+   }
+
    file = fopen(filename, "a");
 
    if (file == (FILE *) NULL)
@@ -53,8 +58,7 @@ int ZoO_storage_write_line
       ZoO_ERROR
       (
          io,
-         "Could not store line '%s' in %s.",
-         line,
+         "Could not store line in storage file %s.",
          filename
       );
 
diff --git a/src/storage/storage.h b/src/storage/storage.h
index c287b23..9eff281 100644
--- a/src/storage/storage.h
+++ b/src/storage/storage.h
@@ -1,14 +1,14 @@
 #ifndef _ZoO_STORAGE_STORAGE_H_
 #define _ZoO_STORAGE_STORAGE_H_
 
-#include "../pipe/pipe_types.h"
+#include <stdio.h>
 
 int ZoO_storage_write_line
 (
    const char filename [const restrict static 1],
    char line [const restrict static 1],
    size_t const line_size,
-   const struct ZoO_pipe io [const restrict static 1]
+   FILE io [const restrict static 1]
 );
 
 #endif