ONT Re: Alpha Graph Exercises

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AGE.  Note 4

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I will on occasion make use of the "Cactus Language" extension
of Peirce's Alpha Graphs, so called because it uses a species
of graphs that are usually called "cacti" by graph theorists.
The last exposition of the cactus syntax that I've written
can be found here:

| Jon Awbrey, "Propositional Equation Reasoning Systems" (PERS)
| PERS.  http://stderr.org/pipermail/inquiry/2003-March/thread.html#126

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