--- math.pl.ORG	2004-01-01 15:15:01.000000000 +0900
+++ math.pl	2014-08-19 20:02:50.828761000 +0900
@@ -1432,6 +1432,7 @@
 	    while ($pre_test =~ s/(($O|$OP)\d+($C|$CP))(.*)\1/$4/) {};
 	    $use_all = 1 if ($pre_test=~s/($O|$OP)\d+($C|$CP)//);
 	    if (!$use_all) {
+		$pre_test = $pre_text;
 	        while ($pre_test =~ s/\\begin(($O|$OP)\d+($C|$CP))(.*)\\end\1/$4/){};
 		$use_all = 1 if ($pre_test=~s/\\(begin|end)($O|$OP)\d+($C|$CP)//);
 	    };