“…The predicate requests(a, s) holds if actor a wants service s fulfilled, while provides(a, s) holds if actor a has the capability to fulfill service s. The predicate delegate(exec, a, b, s) holds if actor a delegates 6 Other predicates are used to define properties that will be used during formal analysis. The predicates delegateChain (exec, a, b, s) and trustChain(exec, a, b, s) hold if there is a delegation and a trust chain respectively, between actor a and actor b.…”