Dear all, I found out that sometimes match fails even when the pattern matches. This depends on the canonical ordering. Imagine that we have an expression that looks like x^5*y^(-1). and a pattern that looks like ($0)^(-1)*x^($2). Then the first thing that is attempted is to match x^5 with ($0)^(-1). This match will fail, however, the side effect of this match will be that the repl_lst now contains $0==x. This repl_lst will prevent the match of y^(-1) to ($0)^(-1) to succeed. A patch is in CVS. I also patched 1.3. Best, Chris