Goal:
    z : Z  z0 : Z  H : (z <= z0)%Z
  ============================
   ((z0 <= z)%Z -> Some z = Some z0)


DEBUG:Going to execute:
do_intro; try do_atom
Level 0: Backtrace:

Tactic failure: congruence failed.
Level 0: Backtrace:

Tactic failure: congruence failed.
Level 0: Backtrace:

No applicable tactic.