generated at
Polytypism
https://en.wikipedia.org/wiki/Polymorphism_(computer_science)#Polytypism
https://en.wikipedia.org/wiki/Generic_programming#Functional_languages
http://www.cse.chalmers.se/~patrikj/poly/PolyH/
https://zenzike.com/posts/2010-12-10-from-polymorphic-to-polytypic.html