Hi Heinrich, I didn't see any mature zipper libraries to efficiently manipulate trees. Can you point me to any mature libs ? Aside from that, there are many reasons why I would represent trees using sequence. The major one is that many GA operations like 2 point crossover and mutation are trivial if we represent the genome in vectors or sequence instead of trees. The downside is the cost of the translation of sequences back to trees. -- Regards, Gabi http://bugspy.net