@Contract(pure = true)
  public static @Unmodifiable @NotNull <T> Set<T> union(@NotNull Set<? extends T> set, @NotNull Set<? extends T> set2) {
    return union((Collection<? extends T>)set, set2);
  }
@Contract(pure = true)
  public static @Unmodifiable @NotNull <T> Set<T> union(@NotNull Set<? extends T> set, @NotNull Set<? extends T> set2)