return new Chopper() {
        @Override
        Optional<String> chop(String str) {
          return i.chop(str).or(you.chop(str));
        }
      };
    }

    abstract Optional<String> chop(String str);

    static Chopper suffix(String suffix) {
      return new Chopper() {
        @Override
        Optional<String> chop(String str) {
          if (str.endsWith(suffix)) {

consultant.aero
consulting
consulting.aero
contact
contagem.br
contractors
control.aero
convex.site
cooking
cool
coolblog.jp
coop
coop.ar
coop.br
coop.ht
coop.in
coop.km
coop.mv
coop.mw
coop.py
coop.rw
cooperativa.bo
copro.uk
corsica
cosenza.it
couchpotatofries.org
council.aero
country
coupon
coupons
courses
coz.br

          }
        };
    assertThrows(IllegalStateException.class, iter::hasNext);
  }

  // Technically we should test other reentrant scenarios (9 combinations of
  // hasNext/next/peek), but we'll cop out for now, knowing that peek() and
  // next() both start by invoking hasNext() anyway.

  private static final ImmutableSet<String> VALID_NAME =
      ImmutableSet.of(
          // keep-sorted start
          "123.cn",
          "8server.shop",
          "a" + DELTA + "b.com",
          "abc.a23",
          "biz.com.ua",
          "f--1.com",
          "f--o",
          "f-_-o.cOM",
          "f11-1.com",
          "fOo",
          "f_a",