Goal:
    A : Type  n : nat  P : A → bool  d : A
  ============================
   (true → S n < 0 → ∃ x : A, d = x ∧ P 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"