The following is also not correct. if k not in mem: mem += [k] if k in mem: # not the same than "else" here if np.random.rand() >

The following is also not correct. if k not in mem: mem += [k] if k in mem: # not the same than "else" here if np.random.rand() > p: mem.remove(k) Your final solution is indeed correct, and I think more elegant than what we had in our paper [I am one of the authors].