1 files changed, 1 insertions, 1 deletions
diff --git a/README.md b/README.md
index bacfd06..7d773fc 100644
--- a/README.md
+++ b/README.md
@@ -31,7 +31,7 @@ or can be interpreted with the [ABCMachine][abc-github] project.
                   |  <Op1> <Expression>
                   |  <Op2> <Expression>
 
-<Op1>            ::= '~'
+<Op1>            ::= '~' | '!'
 
 <Op2>            ::= '+' | '-' | '*' | '/' | '%' | '==' | '||' | '&&'