This paper introduces the notion of veto number that can be associated with agreement problems. An agreement problem has veto number ℓ when ℓ is the minimal number of processes
that control the allowed decision values, i.e., if each of them changes its mind on the value it proposes, then it forces
deciding on a different value. The paper presents and investigates this concept.
Keywords Agreement problem - Asynchronous system - Consensus - Distributed algorithm - One shot problem - Process crash - Failure detector