Goal:
  
  A : Type
  B : Type
  f : A → B
  H : ∀ l : list A, nth_error (map f l) 0 = option_map f (nth_error l 0)
  l : list A
  ============================
   (nth_error (map f l) 1 = option_map f (nth_error l 1))


DEBUG:Going to execute:
apply : eq_sym ; trivial
Level 0: Backtrace:

Proof is not complete.
Level 0: Backtrace:

Proof is not complete.