Goal:
  
  A : Type
  i : positive
  IHi : forall (x : A) (m : tree A), get i (set i x m) = Some x
  x : A
  ============================
   (get (xO i) (set (xO i) x Empty) = Some x)


DEBUG:Going to execute:
rewrite set_Empty
DEBUG LTAC Evaluated term: set_Node
DEBUG LTAC Evaluated term: set_Node