public void setPreserved() {
		if (!preserved) {
			preserved = true;
			Identifier ptr = this;
			while (ptr != null) {
				ptr.setSinglePreserved();
				ptr = ptr.left;
			}
			ptr = right;
			while (ptr != null) {
				ptr.setSinglePreserved();
				ptr = ptr.right;
			}
		}
	}