A Dyck shift and a Motzkin shift are mathematical models for constraints on genetic sequences. In terms of the theory of symbolic dynamics, neither of the Dyck shift nor the Motzkin shift is sofic. In terms of the mathematical language theory, they are non-regular and context free languages. Therefore we can not use the Perron-Frobenius theory to calculate capacities of these constraints. O. Milenkovic has shown that the DSV (Del`est-Sch