Contract Entailment. Contract entailment is a relation ≤ such that, when c ≤ d holds, each value that satisfies c can be used where a value that satisfies d is expected. When c and d are flat contracts, ≤ boils down to the set-theoretic inclusion between the values that satisfy the respective predicates. For example, flat_c (≥ 3) ≤ flat_c (≥ 0) since every number greater than or equal to 3 is also greater than or equal to 0. To define entailment when c and d are session contracts, it helps to recall the analogy of contracts as specifications for the messages that can be sent on and received from a session endpoint. In this case, c ≤ d holds if two conditions are satisfied:
Contract Entailment. Contract entailment is a relation ⩽ such that, when c ⩽ d holds, each value that satisfies c can be used where a value that satisfies d is expected. When c and d are flat contracts, ⩽ boils down to the set-theoretic inclusion between the values that satisfy the respective predicates. For example, since every number greater than or equal to 3 is also greater than or equal to 0. To define entailment when c and d are session contracts, it helps to recall the analogy of contracts as specifications for the messages that can be sent on and received from a session endpoint. In this case, c ⩽ d holds if two conditions are satisfied:
