Goal:
    z : Z  z0 : Z  z1 : Z  H : (z1 <= z)%Z \/ (z1 <= z0)%Z
  ============================
   (z1 <= Z.max z z0)%Z


DEBUG:Going to execute:
<Coq.Init.Tauto.is_conj> flags X1; elim id; do 2 intro; clear id