Anastasia Lisitsyna got in touch with us earlier this year to ask if we would be willing to be the ‘customer’ for her graduation project from Higher School of Economics Lyceum in Moscow - the project was an ambitious reference book of Welsh grammar tables, which you can now see (in both English and Russian) here:
https://drive.google.com/drive/folders/1yYNDDvSok3A_T9hmN8TWjFVBrzN-dkfh?usp=sharing
@CatrinLliarJones - one for the email? 
Brilliant … and on page 16 I’ve already learnt something new. 
Very useful! Great work Anastasia.
Hmm… Interesting, but I’ve just come across something that’s given me pause for thought - I might need to check some more formal grammars… Foot of p.11 reads to me that feminine nouns after yn (e.g. Mae hi’n) don’t soft-mutate, which feels… wrong. I tried Mae hi’n *prifathrawes and Mae hi’n *dynes glên on the University of Bangor’s Cysill ar-lein, in case this was a rule of more literary grammar that I wasn’t familiar with, but it objected to both. Or do others think I’m reading into it an implication that wasn’t intended?
Wow! Very impressive - thank you for sharing! A massive amount of work has gone into that!
You’re certainty right that it would be ‘mae hi’n brifathrawes’…
I think it’s more an omission - that ‘linking word yn ->’ isn’t also listed under ‘feminine’… So it implies that doesn’t work for feminine nouns, rather than actually stating it…
Oh my God, am I having a conversation about grammar?! 
When you speak in this way about your relationship with grammar, @aran, I am always reminded of Winston Smith’s relationship with Big Brother, and his conversation (in the film) with his interrogator O’Brien (the great Welshman Richard Burton’s final role):
O’B: Tell me truthfully, Winston - what are your feelings about Big Brother?
WS : I hate him!
O’B: (calmly but earnestly) You must love him, Winston…you must love him.
And in the end, he does! 
The interesting thing is that my daughter saw this post & commented on my usage of “feels… wrong” & I was of course completely unable to convey to her how, once you’ve got used to doing so, failing to soften after yn just kind of leaves a weird taste in your mouth. Who knew that grammar could feel icky?
I couldn’t imagine a more perfect analogy. I know exactly how Winston felt 
Speaking as someone who genuinely loves grammar, I love this! There are (if I can be churlish for a second) some errors in there (it’d probably be too churlish to start listing them here) but that doesn’t detract from the achievement. Chwarae teg iddi!
Очень интересно и полезно спасибо. Diolch!
… which means “Very interesting and helpful thanks” 
Shwmae i bawb!
Thank you very much for your comments and the discussion. I appreciate all of them. In regard to what @RichardBuck says, is it “mae hi’n brifathrawes” in the end? It would be nice to make sure so I can make necessary changes.
Yes, that’s my understanding - softening after predicative yn is for all nouns (and adjectives) regardless of gender. I’m not at home so haven’t checked my formal grammar, but that’s consistent with the University of Bangor tool & with @aran’s reply above.
Gwych! Diolch yn fawr iawn!
So very useful and reminding me, in the first few pages of some grammar rules I have retained from my schooldays, nearly 60 years ago! Thanks Aran and Catrin but “Diolch yn fawr iawn” to Anastasia.