2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/30671We present the first explicit, and currently simplest, randomized algorithm for 2-process wait-free test-and-set. It is implemented with two 4-valued single writer single reader atomic variables. A test-and-set takes at most 11 expected elementary steps, while a reset takes exactly 1 elementary step. Based on a finite-state analysis, the proofs of correctness and expected length are compressed into one table.9 pages, 4 figures, LaTeX source; SubmittedDistributed, Parallel, and Cluster ComputingC.2; F.2.2text