Contracts as games on event structures

A crucial notion arising in this setting is that of agreement: a participant agrees on a set of contracts if she has a strategy to reach her goals in all the plays conforming to her strategy (or to make another participant sanctionable for not honouring an obligation). Another relevant notion is protection: a participant is protected by her contract when she has a strategy to avoid losing in any contexts, even in those where she has not reached an agreement. We study conditions for obtaining agreement and protection, and we show that these properties mutually exclude each other in a certain class of contracts. We then relate the notion of agreement in contracts with that of compliance in session types. In particular, we show that compliance corresponds to the fact that eager strategies lead to agreement.