Goal:
    A : Type  j : positive  m1 : tree' A  m2 : tree' A  H : xH <> xI j
  ============================
   (get xH (Node (Nodes m1) None (rem' j m2)) = 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.