On the projection method for protocol verification

Shankar and Lam propose a projection method for protocol verification. They claim that the method guarantees the faithfulness of the safety and liveness properties of a protocol system. Although not clearly defined, “faithfulness” (as implied in many places in their article) means “the image protocol system is live (respectively, safe) if and only if the original protocol system is live (respectively, safe).” This paper shows that the “only if” part is not true for certain liveness properties and suggests a remedy.