Started building a toy CAS system called `casual`, in Rust, with S-Expr
input/output syntaxt. Following

* Cohen CAS books
* `expreduce` (golang) documentation
* Norvig LISP book term re-writing chapter
* Hanson and Sussman "Software Design for Flexibility" pattern matching sections and syntax

Another classic integral tool: [`SAINT`](http://logical.ai/auai/doc/doc-calculus.html)