# Draw a edges between two mentities
	fun draw_edge(from, to: MEntity): DotEdge do
		if edges.has(from, to) then return edges[from, to].as(not null)
		if edges.has(to, from) then return edges[to, from].as(not null)
		var nfrom = draw_node(from)
		var nto = draw_node(to)
		var edge = new DotEdge(nfrom, nto)
		edges[from, to] = edge
		graph.add edge
		return edge
	end