Hello Hugo, I know casting to an ex is a solution (would not call it ``the solution'' though: ``the solution'' is editing the source files and recompiling GiNaC). It is not natural that you can use the method subs(lst) to an expression but not to a function. So, unless it turns out to be some weird compiler error in my gcc-version, I would rather see this fixed in future GiNaC versions than condemning future generations to having to use this cast. Greetings, Chris