Goal:
  
  A : Type
  a : A
  l : list A
  P : nat → A → Type
  x : A
  IHl : ∀ (n : nat) (x : A),
          Alli P 0 (List.rev l) → nth_error l n = Some x → P (#|l| - S n) x
  Alll : Alli P 0 (List.rev l)
  X : P #|l| a
  ============================
   (P #|l| a)


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"