Which does that and that's what Llang suggests as well, I remember 2 in some power in his formula. I myself find the separate one-bit counter easier to understand: each side counts pages, but they don't need the full number, only the difference between their counters and the difference can be at most one, so one bit is sufficient. If the counters are same, the actors are on the same page, if they are different, then the writer is one page ahead.