On the Cyclic Assumption of the Cow-Path Search Algorithm

In the cow-path problem, a cow must find a goal lying at an unknown distance on one of w paths connected only at the origin, and performance is measured by competitive ratio. Kao, Reif and Tate designed an efficient randomized algorithm in which the cow visits the paths in a fixed cyclic order. They proved the algorithm is optimal for w=2, and subsequently Kao, Ma, Sipser and Yin proved its optimality for all w, with a claim that no algorithm does better than the best cyclic one. This note provides a detailed proof of that claim.