Building Problem Solvers by Kenneth D. Forbus and Johan de Kleer: http://www.qrg.northwestern.edu/BPS/readme.html

Paradigms of Artificial Intelligence Programming by Peter Norvig: https://github.com/norvig/paip-lisp

Engineer's Journey, tuturto's blog: https://engineersjourney.wordpress.com/

Blog entry about solving n-queens puzzle with general problem solver: https://engineersjourney.wordpress.com/2018/03/09/n-queens-puzzle-solved-in-hy-and-cps/