tildegraph

  http://www.academia.edu/7036052/The_tildegraph_concept_in_sdfsys
http://phd.samuelfreeman.me.uk/thesis-6-2.html#6.2.5
http://phd.samuelfreeman.me.uk/thesis-6-2.html#6.2.6
http://phd.samuelfreeman.me.uk/thesis-7.html#7.4