private void moveIncomingArcs( Node from, Node to ) throws MVDException
	{
		while ( !from.isIncomingEmpty() )
		{
			Arc a = from.removeIncoming( 0 );
			to.addIncoming( a );
		}
		// check if node is now isolated
		if ( from.indegree()==0&&from.outdegree()==0 )
			from.moveMatches( to );
	}