- https://cs.brown.edu/~rt/gdhandbook/
- http://cs.brown.edu/~rt/papers/gd-tutorial/gd-constraints.pdf
- http://graphics.stanford.edu/courses/cs448b-02-winter/lectures/treesgraphs/tree.graph.pdf
- http://www.cs.unc.edu/techreports/89-034.pdf
- https://en.wikipedia.org/wiki/Graph_drawing
- http://www.graphviz.org/Documentation/
