From f23d7365a67c9b73a767162b728ed3fbdb3b79ac Mon Sep 17 00:00:00 2001
From: Masaya Tojo <masaya@tojo.tokyo>
Date: Sat, 16 Jul 2022 15:35:48 +0900
Subject: lists: perm: Add guards.

---
 lists/perm.lisp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lists/perm.lisp b/lists/perm.lisp
index e1d8c77..4668a2b 100644
--- a/lists/perm.lisp
+++ b/lists/perm.lisp
@@ -1,6 +1,8 @@
 (in-package "ACL2")
 
 (defun perm (x y)
+  (declare (xargs :guard (and (true-listp x)
+                              (true-listp y))))
   (cond
     ((atom x) (atom y))
     ((member-equal (car x) y)
-- 
cgit v1.2.3