@Override
	public boolean equals(Object obj) {
		if (this == obj) return true;
		if (obj == null) return false;
		if (getClass() != obj.getClass()) return false;
		PersistentSet<?> other = (PersistentSet<?>) obj;
		if (set == null) {
			if (other.set != null)
				return false;
		} else if (!set.equals(other.set))
			return false;
		return true;
	}