public void clear() {
      multimap.clear();
    }
  }

  /**
   * Returns a multimap containing the mappings in {@code unfiltered} whose keys satisfy a
   * predicate. The returned multimap is a live view of {@code unfiltered}; changes to one affect
   * the other.
   *
   * <p>The resulting multimap's views have iterators that don't support {@code remove()}, but all

        return set1.contains(element) ^ set2.contains(element);
      }
    };
  }

  /**
   * Returns the elements of {@code unfiltered} that satisfy a predicate. The returned set is a live
   * view of {@code unfiltered}; changes to one affect the other.
   *
   * <p>The resulting set's iterator does not support {@code remove()}, but all other set methods

    Iterator<String> iterator = asList("one", "two", "three", "four", "five").iterator();
    try {
      Iterators.getOnlyElement(iterator);
      fail();
    } catch (IllegalArgumentException expected) {
      assertThat(expected)
          .hasMessageThat()
          .isEqualTo("expected one element but was: <one, two, three, four, five>");
    }
  }