A simple bivalency proof that t-resilient consensus requires t+1 rounds
Marcos K. Aguilera, Sam Toueg · Information Processing Letters · 1999
We use a straightforward bivalency argument borrowed from Fischer et al. (1985) to show that in a synchronous system with up to t crash failures solving consensus requires at least t+1 rounds. The proof is simpler and more intuitive than the traditional one: It uses an easy forward induction rather than a more complex backward induction which needs the induction hypothesis several times.