Goal:
    z : Z  z0 : Z  z1 : Z  H : (z1 <= z)%Z \/ (z1 <= z0)%Z  H0 : (z1 <= z)%Z
  ============================
   (z1 <= Z.max z z0)%Z


DEBUG:Going to execute:
<coq-core.plugins.ltac::clear@0> $1