Example (Delivery Robot): A delivery robot delivers items a, b, c, d, e and each delivery activity may take place at one of the time instants t1, t2, t3, t1. Denote A to be the variable representing the time instant that delivery activity for a occurs, and so on. The domains of variables A, B, C, D, E are dom(A) t, t2, t3, t4 dom(B) t1, t2,t3, t4 dom(C)- {ti,t2, ts, t4) dom(D)- t1, t2, t3, t4 dom(E)-{t1, l2, ts, t4) Suppose we have the following constraints to be satisfied {(B1), (C4), (A-D), (E