type GraphReducer interface {
	graph.Directed
	graph.EdgeRemover
}

func TransitiveReduce(g GraphReducer) {
	uit := g.Nodes()
	for uit.Next() {
		uid := uit.Node().ID()
		vit := g.From(uid)
		for vit.Next() {
			w := traverse.DepthFirst{Traverse: func(e graph.Edge) bool {
				xid := e.To().ID()
				if g.HasEdgeFromTo(uid, xid) {
					g.RemoveEdge(uid, xid)
				}
				return true
			}}
			w.Walk(g, vit.Node(), nil)
		}
	}
}