Hi all, I'm afraid I have quite a newbie question. I have followed the tutorials, especially tutorial 4, but I'm still overwhelmed by the functionality of ECJ. Therefore I would like your advise on the following: I have a problem that I can represent as a tree and would like to solve using a genetic algorithm. The number of function nodes is limited (lets say they are the arithmetic operators of tutorial 4). The leaves can be instances of a limited alphabet (say A,B,C) that is different for each problem instance. A solution I'm looking for could for instance be '+ A (- B (* C A )'. When I look at the type of problem of tutorial 4 then this is solving a formula with 2 variables and 3 operators. In my problem I have an unknown number of variables. So my question is how do I go about solving this? I can't create classes beforehand since I don't know the (size of the) alphabet beforehand. I could create one class (say AlphabetInstance) but how do I initialize each instance with a value from the alphabet while not breaking the ECJ framework guidelines. So, in short, my question is how to model a problem with an unknown number of variables and instances of these variables. Thank you in advance for any replies. Joos Buijs PhD Student Eindhoven University of Technology