BitSet getClique( Arc selected )
	{
		BitSet bs = new BitSet();
		if ( incoming.size() > 0 )
		{
			ListIterator<Arc> iter = incoming.listIterator();
			while ( iter.hasNext() )
			{
				Arc a = iter.next();
				if ( !a.versions.intersects(selected.versions) )
					bs.or( a.versions );
			}
		}
		// else it's the start node and the clique is empty
		return bs;
	}