what i need is ALL the lists which you can make by interleaving elements from listA and listB
why is another question entirley, i don't really know except that its for some form of memory experiment, the guy i work for asked me for a script to do all the permutations of a list which i gave him and then he asked me for this
and yes your right the brute force method of just generating all the permutations and then selecting the ones i'm interested was assumption on my part of the easiest way to do it