diff --git a/subjects/isnegative/README.md b/subjects/isnegative/README.md
index 9dc0803e..faa7a0bc 100644
--- a/subjects/isnegative/README.md
+++ b/subjects/isnegative/README.md
@@ -37,3 +37,7 @@ F
 T
 $
 ```
+
+### Notions
+
+- [01-edu/z01](https://github.com/01-edu/z01)
diff --git a/subjects/printalphabet/README.md b/subjects/printalphabet/README.md
index 02f1983e..20911807 100644
--- a/subjects/printalphabet/README.md
+++ b/subjects/printalphabet/README.md
@@ -13,3 +13,7 @@ $ go run .
 abcdefghijklmnopqrstuvwxyz
 $
 ```
+
+### Notions
+
+- [01-edu/z01](https://github.com/01-edu/z01)
diff --git a/subjects/printcomb/README.md b/subjects/printcomb/README.md
index a98f0325..bb2dee3d 100644
--- a/subjects/printcomb/README.md
+++ b/subjects/printcomb/README.md
@@ -36,6 +36,10 @@ $ go run . | cat -e
 $
 ```
 
-`000` or `999` are not valid combinations because the digits are not different.
+- `000` or `999` are not valid combinations because the digits are not different.
 
-`987` should not be shown because the first digit is not less than the second.
+- `987` should not be shown because the first digit is not less than the second.
+
+### Notions
+
+- [01-edu/z01](https://github.com/01-edu/z01)
diff --git a/subjects/printcomb2/README.md b/subjects/printcomb2/README.md
index 76119a3e..620b46d7 100644
--- a/subjects/printcomb2/README.md
+++ b/subjects/printcomb2/README.md
@@ -35,3 +35,7 @@ $ go run . | cat -e
 00 01, 00 02, 00 03, ..., 00 98, 00 99, 01 02, 01 03, ..., 97 98, 97 99, 98 99$
 $
 ```
+
+### Notions
+
+- [01-edu/z01](https://github.com/01-edu/z01)
diff --git a/subjects/printcombn/README.md b/subjects/printcombn/README.md
index 35585d57..0e3f6eb2 100644
--- a/subjects/printcombn/README.md
+++ b/subjects/printcombn/README.md
@@ -8,7 +8,7 @@
 
 below are your references for the **printing format** expected.
 
-- (for n = 1) '0, 1, 2, 3, ...8, 9'
+- (for n = 1) '0, 1, 2, 3, ..., 8, 9'
 
 - (for n = 3) '012, 013, 014, 015, 016, 017, 018, 019, 023,...689, 789'
 
@@ -45,3 +45,9 @@ $ go run .
 012345678, 012345679, ..., 123456789
 $
 ```
+
+> Be mindful of your program efficiency to avoid timeouts.
+
+### Notions
+
+- [01-edu/z01](https://github.com/01-edu/z01)
diff --git a/subjects/printdigits/README.md b/subjects/printdigits/README.md
index 40381764..edb285b7 100644
--- a/subjects/printdigits/README.md
+++ b/subjects/printdigits/README.md
@@ -13,3 +13,7 @@ $ go run .
 0123456789
 $
 ```
+
+### Notions
+
+- [01-edu/z01](https://github.com/01-edu/z01)
diff --git a/subjects/printnbr/README.md b/subjects/printnbr/README.md
index a32d5116..34b332a0 100644
--- a/subjects/printnbr/README.md
+++ b/subjects/printnbr/README.md
@@ -40,3 +40,8 @@ $ go run .
 -1230123
 $
 ```
+
+### Notions
+
+- [01-edu/z01](https://github.com/01-edu/z01)
+- [numeric types](https://golang.org/ref/spec#Numeric_types)
diff --git a/subjects/printreversealphabet/README.md b/subjects/printreversealphabet/README.md
index f15e0b17..a1edc8c7 100644
--- a/subjects/printreversealphabet/README.md
+++ b/subjects/printreversealphabet/README.md
@@ -15,3 +15,7 @@ $ go run .
 zyxwvutsrqponmlkjihgfedcba
 $
 ```
+
+### Notions
+
+- [01-edu/z01](https://github.com/01-edu/z01)