diff --git a/arith.modal b/arith.modal
index 071345d..45deefd 100644
--- a/arith.modal
+++ b/arith.modal
@@ -337,4 +337,4 @@
 -- (str (div (mul a b) c))
 
 -- (mul (nat>neg (nat 13)) (nat>neg (nat 7)))
-(str (mul (int 13) (int 7)))
+(str (mul (int -133) (int 77)))