https://www.reddit.com/r/learnwelsh/comments/mrov7t/welsh_grammar_all_about_yn_verbal_aspects/

https://duome.eu/chrisaldrich/progress

Duolingo progress with words and grammar tabs

https://web.archive.org/web/19990501205918/http://www.madog.org/geiriadr.html

J.R.R. Tolkien purchased a copy of John Morris-Jones's (1864-1929) A Welsh Grammar when he was at Exeter.

https://archive.org/search.php?query=A%20Welsh%20grammar%20%3A%20historical%20and%20comparative

timestamp [8:13]