Goal:
    A : Type  j : positive  m : tree' A  H : xH <> xI j
  ============================
   (get xH (Node Empty None (rem' j m)) = None)


DEBUG:Going to execute:
rewrite gNode; auto; apply IHi; congruence
Level 0: Backtrace:

Tactic failure: congruence failed.
Level 0: Backtrace:

Tactic failure: congruence failed.