}
  }

  @CollectionSize.Require(ZERO)
  public void testEmptySetFirst() {
    assertThrows(NoSuchElementException.class, () -> sortedSet.first());
  }

  @CollectionSize.Require(ZERO)
  public void testEmptySetLast() {
    assertThrows(NoSuchElementException.class, () -> sortedSet.last());
  }

  @CollectionSize.Require(ONE)
  public void testSingletonSetFirst() {
    assertEquals(a, sortedSet.first());
  }