private Set<String> getRankSame(Collection<Line> lines) {
		final Set<String> rankSame = new HashSet<String>();
		for (Line l : lines) {
			if (l.hasEntryPoint()) {
				continue;
			}
			final String startUid = l.getStartUid();
			final String endUid = l.getEndUid();
			if (isInCluster(startUid) && isInCluster(endUid)) {
				final String same = l.rankSame();
				if (same != null) {
					rankSame.add(same);
				}
			}
		}
		return rankSame;
	}