diff --git a/README.md b/README.md
index 29b96bc..1f67482 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,8 @@ This file describes **transition function** of automaton or **action function**
  - First line contain all elements of automaton (or act). Here it\`s 7. Element name can consist of more than one letter, but without spaces.
  - Next lines contains action on specific semigroup element. For example, second line means: `1*s1 = 1`,  `1*s2 = 2`, etc.
 
+If you don\`t want specify some value of transition function, just print `_` in the line like this: `s3 2 _ 2 5 _ _ 7`.
+
 #### Compilation
 
 If you want to recompile this, you need **Haskell Stack**.