Goal:
    A : Type  P : nat → A → Type  l' : list A  n : nat
  ============================
   (Alli P n l' → Alli P n 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"