Additional comments on a problem in concurrent programming control

Professor Dijkstra's ingenious construction [Solution of a Problem in Concurrent Programming Control, Comm. ACM 8 (Sept. 1965), 569] is not quite a solution to a related problem almost identical to the problem he posed there, and Mr. Hyman's "simplification" for the case of two computers ]Comm. ACM 9 (Jan. 1965), 45] hardly works at all. I hope that by this letter I can save people some of the problems they would encounter if they were to use either of those methods