Goal:
  
  G : t
  HI : invariants
  z : Z
  z0 : Z
  H : 0 <= z
  cstr : 0 <= Z.of_nat (to_label (Some z))
  cstr0 : 0 <= Z.of_nat (to_label (Some z0))
  z1 : Z
  H1 : Z.of_nat (to_label (Some z)) < Z.of_nat (to_label (Some z0)) /\
       z1 = Z.of_nat (to_label (Some z0)) \/
       Z.of_nat (to_label (Some z0)) <= Z.of_nat (to_label (Some z)) /\
       z1 = Z.of_nat (to_label (Some z))
  z2 : Z
  H2 : z < z0 /\ z2 = z0 \/ z0 <= z /\ z2 = z
  ============================
   (z2 = z1)


DEBUG:Going to execute:
idtac