Goal:
    A : Type  a : A  m : tree' A  IHm : exists i : positive, get' i m <> None
  ============================
   (exists i : positive, get' i (Node011 a m) <> None)


DEBUG:Going to execute:
destruct IHm as [p H]
Level 0: Backtrace:

The variable IHm was not found in the current environment.