Could I just check my understanding of a couple of soft mutations, please?
Mae o’n ddyn mawr
Dyn → ddyn, because it’s a noun following a linking ‘yn’, therefore the gender and number is irrelevant.
Daeth y ddau
dau → ddau. I’m not sure about this one, because dau is masculine and therefore shouldn’t(?) mutate after y. Is it because it’s following a short form verb and there’s no linking ‘yn’? (Though I thought that was for direct objects, not for subjects…) Or is dau not masculine here?
I can’t find anything else that looks relevant in the list of mutation causes (there are 29 in the BBC Basic rules of grammar guide…) What am I missing, please?