--- loncom/homework/lonmaxima.pm	2017/03/06 17:01:59	1.33
+++ loncom/homework/lonmaxima.pm	2017/03/07 16:04:35	1.36
@@ -1,7 +1,7 @@
 # The LearningOnline Network with CAPA
 # Interface routines to MAXIMA CAS
 #
-# $Id: lonmaxima.pm,v 1.33 2017/03/06 17:01:59 raeburn Exp $
+# $Id: lonmaxima.pm,v 1.36 2017/03/07 16:04:35 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -155,10 +155,10 @@ sub maxima_eval {
 
 sub compareterms {
     my ($socket,$terma,$termb)=@_;
-    if ($terma =~ m{[.*^/\s]+(|\(\s*\((|[^(]+))$}) {
+    if ($terma =~ m{\(\s*\([^)]*$}) {
         return 'Error: blacklisted';
     }
-    my $difference=$terma.'-('.$termb.')';
+    my $difference='('.$terma.')-('.$termb.')';
     if (&blacklisted($difference)) { return 'Error: blacklisted'; }
     my $reply=&maximareply($socket,'trigsimp(trigreduce('.$difference.'));');
     if ($reply=~/^\s*0\s*$/) { return 'true'; }