Goal:
    A : Type  j : positive  m1 : tree' A  a : A  m2 : tree' A  H : xH <> xI j
  ============================
   (get xH (Node (Nodes m1) (Some a) (rem' j m2)) = Some a)


DEBUG:Going to execute:
<coq-core.plugins.cc::cc@0> $1