Nodes in the original graph have a layer and a reference to the original
node. "dummy nodes" have a link to the parent and child of the edge their on
in the original dag, as well as their actual layer. Given that duplicate
edges aren't allowed, this uniquely defines each dummy node.
the NodeDatum used for layered sugiyama layouts
Nodes in the original graph have a layer and a reference to the original node. "dummy nodes" have a link to the parent and child of the edge their on in the original dag, as well as their actual layer. Given that duplicate edges aren't allowed, this uniquely defines each dummy node.