Goal:
  
  A : Type
  p : nat → A → bool
  q : nat → A → bool
  n : nat
  a : A
  l : list A
  hpq : ∀ (i : nat) (x : A), p i x → q i x
  IHl : ∀ n : nat, alli p n l → alli q n l
  pna : is_true (p n a)
  a' : is_true (alli p (S n) l)
  ============================
   (is_true (alli p (S 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"