mathematics numerical expression Algebraic Reverse Polish notation (RPN)

https://opentextbc.ca/businesstechnicalmath/ 

Business/Technical Mathematics 

https://opentextbc.ca/businesstechnicalmath/chapter/1-2/

https://hackaday.com/2017/10/24/reverse-polish-notation-and-its-mildly-confusing-elegance/

https://www.hpmuseum.org/