Goal:
  
  A : Type
  B : Type
  f : A → B
  a : A
  l : list A
  IHl : ∀ n : nat, mapi_rec (λ _ : nat, f) l n = map f l
  n : nat
  ============================
   (f a :: map f l = f a :: map f l)


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"