From 98bff1e5e282d6f4a3ba08d0f25160eda2593602 Mon Sep 17 00:00:00 2001
From: ccremers <ccremers@4f7d145f-a0d4-0310-ae10-d96cc04433c1>
Date: Fri, 20 Aug 2004 15:09:49 +0000
Subject: [PATCH] - Solved the TERM_Hidden issue for the keys in
 termMguSubTerm. Yields   cleaner behaviour for MguSubterm.

---
 src/mgu.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/src/mgu.c b/src/mgu.c
index 0c328f3..b6bfdd3 100644
--- a/src/mgu.c
+++ b/src/mgu.c
@@ -23,6 +23,8 @@
  */
 int mgu_match = 0;
 
+extern Term TERM_Hidden;
+
 void
 showSubst (Term t)
 {
@@ -309,16 +311,21 @@ termMguSubTerm (Term t1, Term t2, int (*iterator) (),
 	      Termlist keylist_new;
 	      Term newkey;
 
-	      keylist_new = termlistShallow (keylist);
 	      newkey = inverseKey (inverses, t2->right.key);
-	      keylist_new = termlistAdd (keylist_new, newkey);
 
-	      // Recurse
-	      flag =
-		flag && termMguSubTerm (t1, t2->left.op, iterator, inverses,
-					keylist_new);
+	      // We can never produce the TERM_Hidden key, thus, this is not a valid iteration.
+	      if (!isTermEqual (newkey, TERM_Hidden))
+		{
+		  keylist_new = termlistShallow (keylist);
+		  keylist_new = termlistAdd (keylist_new, newkey);
 
-	      termlistDelete (keylist_new);
+		  // Recurse
+		  flag =
+		    flag && termMguSubTerm (t1, t2->left.op, iterator, inverses,
+					    keylist_new);
+
+		  termlistDelete (keylist_new);
+		}
 	      termDelete (newkey);
 	    }
 	}