Goal:
    A : Type  B : Type  f : nat → A → B  n : nat  l : list A
  ============================
   (option_map (f n) (nth_error l n) = option_map (f n) (nth_error l n))


DEBUG:Going to execute:
easy
DEBUG LTAC Evaluated term: Nat.add_0_r
DEBUG LTAC Evaluated term: Nat.add_0_r