“…More precisely, we require that the solution u satisfieswhere k , k are given constants fulfilling k Ä k , and w and w are prescribed weight functions on and , respectively. For example, in the case when w Á 1, w Á 0, and k D k , (1.3) represents the conservation of the volume R u.x, t/dx D k , for all t 2 OE0, T, a condition which instead arises naturally from the problem in the framework of a Cahn-Hilliard system (see, e.g., [13, 17] and [18] for a different type of natural mass conservation).The analysis of the abstract theory for this kind of constraint was developed in [19] and motivated from the generalization of concrete problems [20][21][22] (see also [17], where the essential structure of possible constraints has been discussed for Cahn-Hilliard equation). In the abstract approach by [19], the constraint and in particular the barriers k and k in (1.3) are allowed to depend on time.…”