diff --git a/source/Dive_into_Functions.rst b/source/Dive_into_Functions.rst
index 427a4877e8c51595f85ea6bef6a510f829d48fb6..fe648779d38d2ff86b60c97b6ad75a280b07fd68 100644
--- a/source/Dive_into_Functions.rst
+++ b/source/Dive_into_Functions.rst
@@ -497,7 +497,7 @@ Write a program that calculates the similarity of 2 RNA sequences.
   so you have to compare the first base of two sequences and use the matrix to get the similarity
   from the similarity table, on so on for all bases then sum these similarities.
 
-First implementation
+First implementation (list of columns)
 
 .. literalinclude:: _static/code/matrix.py
    :linenos:
@@ -506,7 +506,7 @@ First implementation
 :download:`matrix.py <_static/code/matrix.py>` .
 
 
-Second implementation
+Second implementation (bad variable naming, no documentation)
 
 .. literalinclude:: _static/code/matrix2.py
    :linenos:
@@ -515,7 +515,7 @@ Second implementation
 :download:`matrix2.py <_static/code/matrix2.py>` .
 
 
-Thirs implementation
+Third implementation (dict {(row, col): value})
 
 .. literalinclude:: _static/code/matrix3.py
    :linenos: