void makeEquiv(final Node node1, final Node node2) {
		final Set s1 = equivalent(node1);
		final Set s2 = equivalent(node2);

		if (s1 != s2) {
			s1.addAll(s2);

			final Iterator iter = s2.iterator();

			while (iter.hasNext()) {
				final Node n = (Node) iter.next();
				equiv.put(n, s1);
			}
		}
	}