  We introduce a basic model for contracts. Our model extends event structures
with a new relation, which faithfully captures the circular dependencies among
contract clauses. We establish whether an agreement exists which respects all
the contracts at hand (i.e. all the dependencies can be resolved), and we
detect the obligations of each participant. The main technical contribution is
a correspondence between our model and a fragment of the contract logic PCL.
More precisely, we show that the reachable events are exactly those which
correspond to provable atoms in the logic. Despite of this strong
correspondence, our model improves previous work on PCL by exhibiting a
finer-grained notion of culpability, which takes into account the legitimate
orderings of events.
