Abstract
Proposesd is a controllability condition of a siphon that is composed of two elementary siphons in a class of Petri nets, Systems of Simple Sequential Processes with Resources ((SPR)-P-3). It is shown that, under the condition, an (SPR)-P-3 admits a maximally permissive liveness-enforcing supervisor that is expressed by a set of monitors if every dependent siphon is 2-composed, which can be decided by an algorithm with polynomial complexity.