recent notes and CAS thoughts

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+Started reading "Computer Algebra and Symbolic Computation: Elementary
+Algorithms" by Joel Cohen (2002). This is the somewhat more applied/language
+oriented of two books in a series (the other, "Mathematical Methods",
+apparently dives deeper in to some simplification and manipulation processes).
+
+Currently thinking that implementing a basic schema/s-expr computer algebra
+system would be a good learning exersize, building knowledge and familiarity
+with expression manipulation.
+
+Found [expreduce](https://github.com/corywalker/expreduce), a simple golang
+computer algebra system. Also [mmaclone](https://github.com/jyh1/mmaclone).
+[Blog post](https://corywalker.me/2018/06/03/introduction-to-computer-algebra.html)
+about expreduce, and some documentation of functions which have been
+implemented. Uses syntax, and I assume conventions, of Mathematica.
+
+Via expreduce, found the 'Rubi' integration rule corpus (and basic CAS system)
+by Albert Rich (<http://www.apmaths.uwo.ca/~arich/>). Rich previously worked on
+the CAS built-in to TI-83 calculators!
+
+-----
+
+Specific things learned from CASC:EA book so far:
+
+Internal representations of expressions often involve a stage of simplification
+after parsing an expression. For example, in product expressions, can simplify
+with constraint that none of the members are themselves product expressions,
+and that there is only one rational number member, and it is the first member.
+Division and subtraction are substituded for product-and-negative-power and
+sum-and-negative-product. Presumably additional data structures can be used for
+polynomials, etc.
+
+This initial simplification stage, as part of evaluation, reminds me a bit of
+the tokenization vs. grammar parsing stages of compilation. Eg, where does
+tokenization end and parsing begin.
+
+The 'procedure' definition blocks seem similar to Modelica: Input, Output,
+Local Variables, Begin End.