https://drive.google.com/file/d/1aAA-JA ... sp=sharing

I got a bit confused with my explanation of dhá chuaich dhúbha - I meant to say the adjective in the dual is declined like the general plural of the adjective.

Thank you. The poem is very interesting. (The dual too, of course.)

So for nouns
NOM.DU = DAT.SG, including words which don't have a separate dative form (and so in their case NOM.SG=DAT.SG=NOM.DU).
Genitive is GEN.DU = GEN.PL. right? Considering this: https://corkirish.wordpress.com/genitive-dual/.
And it seems that DAT.DU=DAT.SG. (Cf. MSF XIII: "agus greim lena dhá láimh aige").

Adjectives: dual = plural. (In modern language NOM.PL=GEN.PL=DAT.PL.) Plus lenition as required.

Yes, but even in Father Peter's day some uses were falling away. So dhá theanga was frequently found in the nominative dual, but "ar an dá theagain" was always found in his works in the dative dual.

Ceist agam mar gheall ar beirt mhnaoi:

An úsáidtar an fhuirm seo sa ghnáth-chainnte, nú an lé haghaidh an dáin a scrímh sé é? Más féidir beirt mhnaoi a rá (in ionad beirt bhan), an bhfuil fonn 'dídhaonnaithe' (focal gránna, bíodh a fhios agamsa) ag baint leis?

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I'm an intermediate speaker of the Corca Dhuibhne dialect of Irish and also have knowledge on the old spelling
Soir gaċ síar, fé ḋeireaḋ thíar

Is dhá mhnaoi a húsáidaithar sa dán san, agus ní beirt mhnaoi. Ní dó' liom gur ceart an rud é sin - beirt bhan an rud is cirte - sin é a nduairt Dónall Ó hÉalaithe (ná maireann) dom.