Goal:
  
  A : Type
  B : Type
  f : nat → A → B
  g : nat → A → B
  l : list A
  H : ∀ (n : nat) (x : A), f n x = g n x
  ============================
   (∀ (k : nat) (x : A), 0 ≤ k → k < #|l| + 0 → f k x = g k x)


DEBUG:Going to execute:
let rec do_ccl :=
            try do_atom; repeat (do_intro; try do_atom); try arith_congr;
             (solve [ split; do_ccl ])
           in
           (solve [ do_atom | use_hyps; do_ccl ]) ||
             fail "Cannot solve this goal"