https://www.theochem.ru.nl/~pwormer/Knowino/knowino.org/w/index690c-3.html?title=Bibliography:Group_homomorphism&action=edit&redlink=1
Editing Bibliography:Group homomorphism - Knowino
group homomorphismeditingbibliography
https://tetrationforum.org/showthread.php?tid=1604&pid=11062
semi-group homomorphism and tommy's U-tetration
group homomorphismsemitommytetration