bounded-error probabilistic polynomial , I take it it is this that you meant? Which the Alan Turing machine in polynomial time.

In computational complexity theory, BPP, which stands for bounded-error probabilistic polynomial time is the class of decision problems solvable by a probabilistic Turing machine in polynomial time, with an error probability of at most 1/3 for all instances. Informally, a problem is in BPP if there is an algorithm for it that has the following properties: It is allowed to flip coins and make random decisions It is guaranteed to run in polynomial time On any given run of the algorithm, it has a probability of at most 1/3 of giving the wrong answer, whether the answer is YES or NO. Unbelievable the computers they had at Bletchley Park. I hope to visit Bletchley again, as they were fixing it up to look exactly how it was in the 40's.