Goal:
    z : Z  z0 : Z  z1 : Z
  ============================
   (Some (z + z0 + z1)%Z = Some (z + z0 + z1)%Z)


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"