--- loncom/homework/lonmaxima.pm	2010/06/14 11:34:18	1.29
+++ 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 1.29 2010/06/14 11:34:18 www Exp $
+# $Id: lonmaxima.pm,v 1.36 2017/03/07 16:04:35 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -51,7 +51,7 @@ sub maximareply {
 	print $socket &escape($cmd)."\n";
         my $reply=<$socket>;
         chomp($reply);
-        if ($reply=~/^Incorrect/) { $reply='Error: '.$reply; }
+        if ($reply=~/^Incorrect/i) { $reply='Error: '.$reply; }
         return &unescape($reply);
     } else {
         return 'Error: no connection.';
@@ -155,7 +155,10 @@ sub maxima_eval {
 
 sub compareterms {
     my ($socket,$terma,$termb)=@_;
-    my $difference=$terma.'-('.$termb.')';
+    if ($terma =~ m{\(\s*\([^)]*$}) {
+        return 'Error: blacklisted';
+    }
+    my $difference='('.$terma.')-('.$termb.')';
     if (&blacklisted($difference)) { return 'Error: blacklisted'; }
     my $reply=&maximareply($socket,'trigsimp(trigreduce('.$difference.'));');
     if ($reply=~/^\s*0\s*$/) { return 'true'; }