Dear all, I find myself stuck with something which I assume is trivial. I define: m4_define([X], [9]) m4_define([Y], [3]) And I would like to define Z as being the arithmetic sum of X and Y and can seem to get it. I tried several variations of eval but had no success. I understand that all the macros need to be expanded before eval is called but I don't understand how to do it. Any help warmly appreciated. Thanks in advance, Seb.