Open Scope Z_scope.
Definition zlt: forall (x y: Z), {x < y} + {x >= y} := Z_lt_dec.

(* Specifications: *)
Lemma zlt_true:
forall (A: Type) (x y: Z) (a b: A),
x < y -> (if zlt x y then a else b) = a.
Lemma zlt_false:
forall (A: Type) (x y: Z) (a b: A),
x >= y -> (if zlt x y then a else b) = b.