Goal:
    A : Type  B : Type  f : nat → A → B  k : nat  l : list A
  ============================
   (mapi_rec f l k = mapi_rec f l (0 + k))


DEBUG:Going to execute:
easy
DEBUG LTAC Evaluated term: skipn_0
DEBUG LTAC Evaluated term: skipn_0
DEBUG LTAC Evaluated term: skipn_0
DEBUG LTAC Evaluated term: skipn_0