Ehrenfest's urn

[John Keith]

Thanks for the interesting post, this problem is new to me.

Section 2.1 of this article suggests an alternate representation of the urns that may lead to a simpler program. Instead of two lists, one initially empty, one has a single list of (initially) all zeros. At each iteration, the state of a randomly selected element is flipped using NOT. The number of balls in urn "A" is the number of zeros in the list; the number of balls in urn "B" is similarly the number of ones.

My PPL is a bit rusty but it should be fairly simple.