* Returns an immutable set containing the given elements, minus duplicates, in the order each was
   * first specified. That is, if multiple elements are {@linkplain Object#equals equal}, all except
   * the first are ignored.
   */
  public static <E> ImmutableSet<E> of(E e1, E e2) {
    return construct(2, e1, e2);
  }

  /**
   * Returns an immutable set containing the given elements, minus duplicates, in the order each was

              <!-- Keep these timeouts very large because, if we hit the timeout, the tests silently pass :( -->
              <testTimeOut>86400 <!-- seconds --></testTimeOut>
              <testMethodTimeout>1440 <!-- minutes --></testMethodTimeout>
              <!-- Presumably we want watchFileChanges=false here, since we want it for compile: -->
              <extraJvmArgs>-Dgwt.watchFileChanges=false</extraJvmArgs>
            </configuration>