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:
solve
[ trivial
with eq_true
| reflexivity
| symmetry; trivial
| contradiction
| congruence ]