diff --git a/eo-runtime/src/main/eo/org/eolang/math/angle.eo b/eo-runtime/src/main/eo/org/eolang/math/angle.eo
index b1e9d1640b..3e87bd39f9 100644
--- a/eo-runtime/src/main/eo/org/eolang/math/angle.eo
+++ b/eo-runtime/src/main/eo/org/eolang/math/angle.eo
@@ -31,12 +31,12 @@
 # The angle.
 [value] > angle
   value > @
-  # Converts this from radians to degrees
+  # Converts this from radians to degrees.
   angle > in-degrees
     div.
       ^.times 180.0
       pi
-  # Converts this from degrees to radians
+  # Converts this from degrees to radians.
   angle > in-radians
     div.
       $.times pi
diff --git a/eo-runtime/src/main/eo/org/eolang/nan.eo b/eo-runtime/src/main/eo/org/eolang/nan.eo
index 7d3d051e35..5784e5f18a 100644
--- a/eo-runtime/src/main/eo/org/eolang/nan.eo
+++ b/eo-runtime/src/main/eo/org/eolang/nan.eo
@@ -25,7 +25,8 @@
 +package org.eolang
 +version 0.0.0
 
-# Not a number.
+# The `not a number` object is an abstraction
+# for representing undefined or unrepresentable numerical results.
 [] > nan
   number 7F-F8-00-00-00-00-00-00 > @
   $ > floor
@@ -35,25 +36,25 @@
   false > is-integer
   error "Can't convert NaN to i64" > as-i64
 
-  # Tests that $ = x.
+  # Tests that $ value is equal to x.
   false > [x] > eq
 
-  # Tests that $ < x.
+  # Tests that the value $ less than x.
   false > [x] > lt
 
-  # Tests that $ <= x.
+  # Tests that $ less or equal than x.
   false > [x] > lte
 
-  # Tests that $ > x.
+  # Tests that $ value greater than x.
   false > [x] > gt
 
-  # Tests that $ >= x.
+  # Tests that $ greater or equal than x.
   false > [x] > gte
 
   # Returns the multiplication of $ and x.
   ^ > [x] > times
 
-  # Sum of $ and x.
+  # Returns the result of the sum of $ and x.
   ^ > [x] > plus
 
   # Returns the difference between $ and x.
diff --git a/eo-runtime/src/main/eo/org/eolang/negative-infinity.eo b/eo-runtime/src/main/eo/org/eolang/negative-infinity.eo
index fc876453d6..2a6c542f26 100644
--- a/eo-runtime/src/main/eo/org/eolang/negative-infinity.eo
+++ b/eo-runtime/src/main/eo/org/eolang/negative-infinity.eo
@@ -95,7 +95,7 @@
       nan
       ^
 
-  # Quotient of the division of $ by x
+  # Quotient of the division of $ by x.
   [x] > div
     x > value!
     number value > num
diff --git a/eo-runtime/src/main/eo/org/eolang/structs/list.eo b/eo-runtime/src/main/eo/org/eolang/structs/list.eo
index f0c34ddbc2..a35c166711 100644
--- a/eo-runtime/src/main/eo/org/eolang/structs/list.eo
+++ b/eo-runtime/src/main/eo/org/eolang/structs/list.eo
@@ -169,7 +169,7 @@
       accum.with item > [accum item]
 
   # Returns index of the first particular item in list.
-  # If the list has no this item, index-of returns -1
+  # If the list has no this item, index-of returns -1.
   [wanted] > index-of
     ^.reducedi > @
       -1
@@ -182,7 +182,7 @@
           accum
 
   # Returns index of the last particular item in list.
-  # If the list has no this item, returns -1
+  # If the list has no this item, returns -1.
   [wanted] > last-index-of
     ^.reducedi > @
       -1
diff --git a/eo-runtime/src/main/eo/org/eolang/txt/text.eo b/eo-runtime/src/main/eo/org/eolang/txt/text.eo
index c70255859f..4aa44995cb 100644
--- a/eo-runtime/src/main/eo/org/eolang/txt/text.eo
+++ b/eo-runtime/src/main/eo/org/eolang/txt/text.eo
@@ -178,7 +178,7 @@
       ^.index-of substring
 
   # Returns index of `substring` in current `text`.
-  # If no `substring` was found, it returns -1
+  # If no `substring` was found, it returns -1.
   [substring] > index-of
     (string ^.origin.as-bytes).length > self-len!
     string > substr