digraph G {
	margin=0;
	nodesep=0.3;
	ranksep=0.3;
	
	{rank=same;
	1 [shape=circle, label="1", fontcolor=blue, group=l];
	2 [shape=circle, label="2", fontcolor=blue, group=r];
	}
	{rank=same;
	3 [shape=circle, label="3", fontcolor=blue, group=l];
	4 [shape=circle, label="4", fontcolor=blue, group=r, style=bold];
	}
	{rank=same;
	5 [shape=circle, label="5", fontcolor=blue, group=l];
	6 [shape=circle, label="6", fontcolor=blue, group=r];
	}
	
	1->2[label="a", fontcolor=blue];
	1->3[label="b", fontcolor=blue];
	2->3[label="c", fontcolor=blue, dir=back];
	2->4[label="d", fontcolor=blue, dir=back];
	3->4[label="e", fontcolor=blue, dir=back];
	3->5[label="f", fontcolor=blue];
	4->5[label="g", fontcolor=blue];
	5->6[label="h", fontcolor=blue, dir=back];
}