diff --git a/include/plasp/pddl/expressions/NAry.h b/include/plasp/pddl/expressions/NAry.h
index befc097..5529577 100644
--- a/include/plasp/pddl/expressions/NAry.h
+++ b/include/plasp/pddl/expressions/NAry.h
@@ -181,6 +181,7 @@ inline ExpressionPointer NAry<Derived>::simplified()
 	}
 
 	// TODO: recognize tautologies
+	// TODO: introduce handle boolean values
 
 	return this;
 }