Definition int_ind := int_rect.
Variant int_spec (x : int) : int -> Type :=
| ZintNull : int_spec x 0
| ZintPos n : int_spec x n.+1
| ZintNeg n : int_spec x (- (n.+1)%:Z).

Lemma nonzero1z : 1%Z != 0. Proof. by []. Qed.
Definition comMixin := ComRingMixin mulzA mulzC mul1z mulz_addl nonzero1z.