--- researchv9/jerq/sgs/comp/sty.y	2018/04/24 17:22:00	1.1.1.1
+++ researchv9/jerq/sgs/comp/sty.y	2018/04/24 17:33:29	1.1.1.2
@@ -1931,6 +1931,8 @@ register int	s2;
 {
 	register int	i1;
 
+	if(s1 < 0)
+		return  0;
 	for( i1 = s1;  shp[i1].sleft >= 0;  i1 = shp[i1].sleft )
 	{
 		if( i1 == s2  ||  shp[i1].sright == s2 )