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