diff --git a/dev/doc/naming-conventions.tex b/dev/doc/naming-conventions.tex
index 349164948d46..337b9226df75 100644
--- a/dev/doc/naming-conventions.tex
+++ b/dev/doc/naming-conventions.tex
@@ -267,7 +267,7 @@ \subsection{Specific conventions}
 {forall x y:D, op (op' x y) = op' x (op y)}
 
 \itemrule{Idempotency of binary operator {\op} on domain {\D}}{Dop\_idempotent}
-{forall x:D, op x n = x}
+{forall x:D, op x x = x}
 
 \itemrule{Idempotency of unary operator {\op} on domain {\D}}{Dop\_idempotent}
 {forall x:D, op (op x) = op x}