Definition Zmax : forall x_ x_ : Z, Z :=
  fun n m : Z =>
  match (n ?= m)%Z with
  | Datatypes.Eq => m
  | Datatypes.Lt => m
  | Datatypes.Gt => n
  end.

Theorem Zlt_next : forall n m : Z, (n < m)%Z -> m = Zsucc n \/ (Zsucc n < m)%Z.