http://www.ccs.neu.edu/home/matthias/HtDP2e/Draft/part_preface.html
http://poignant.guide/book/chapter-1.html
http://sarabander.github.io/sicp/html/1_002e2.xhtml#g_t1_002e2
https://bartoszmilewski.com/2015/01/07/products-and-coproducts/
aosabook.org/en/index.html