https://www.phon.ucl.ac.uk/courses/spsci/iss/week5.php
https://essentialsoflinguistics.pressbooks.com/chapter/4-5-natural-classes/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3292616/
https://www.thoughtco.com/why-mathematics-is-a-language-4158142
https://landing.athabascau.ca/blog/view/20742/is-language-a-technology
https://www.icr.org/article/genesis-chinese-pictographs/
https://nypost.com/2015/02/08/the-stories-behind-the-letters-of-our-alphabet/
http://mathforum.org/library/drmath/view/56834.html
https://www.phon.ucl.ac.uk/courses/spsci/iss/week5.php
https://essentialsoflinguistics.pressbooks.com/chapter/4-5-natural-classes/
https://www.thoughtco.com/why-mathematics-is-a-language-4158142
https://landing.athabascau.ca/blog/view/20742/is-language-a-technology