diff --git a/doc/concept.sh b/doc/concept.sh
index 008b54a..37bb035 100644
--- a/doc/concept.sh
+++ b/doc/concept.sh
@@ -104,7 +104,6 @@ ifn cond
 
 # cond:
 x
-!x
 x == y
 x != y
 x === y