Just a general point for everybody working their way through this book, no matter where you are in it, about the dual.
The nominative dual has the same form as the dative singular:
ar an bhfuinneoig = on the window
dhá fhuinneoig = two windows
Typically it is formed by taking the genitive and knocking of the final e.
Some words since they have irregular datives, have irregular duals:
ar an mboin = on the cows
dhá bhoin = two cows
However I want to say that the dual is rarer today than the dative, even though both have the same form. There are people who say:
ar an mboin
dhá bhó
Since every number after
a haon sort of insulates the noun after it, you usually don't have to worry about genitive duals or dative duals. Traditionally some nouns had a genitive dual which was different to their nominative dual, but the same as the genitive plural. Examples are súil (g.d. súl), glúin (g.d. glún), bliain (g.d. blian). You'll see these if you read Peadar Ua Laoghaire, Peig, Tomás Ó Criomhthain or other old Munster writers. I can gather a few examples if anybody would like.
Also, quite often, the nominative today is not what it used to be. For example
glúin, used to be
glún, this is because the dative replaced the nominative. Now the usual rule is that the genitive plural is the same as the nominative singular (for weak plurals

). However this often leaves the genitive plural the same as the old nominative singular.
An ghlúin = The knee.
Gealacáin a nglún = The caps of their knees.
Last note:
Adjectives don't have a dual form, even though they have a dative form:
ar an mboin mhóir (móir in Peadar Ua Laoghaire's time)
dhá bhoin mhór
Also adjective don't get inflected after numbers larger than
a haon, they stay in the nominative.
Trí bhád mhóra = The three boats (notice adjective in plural, even though noun is not)
Ramhaí na dtrí mbád mhóra = Oars of the three boats (notice trí, cheithre, chúig and sé take an urú and so do the adjective following them in the genitive plural.)
More complete number rules here:
http://irishlearner.awyr.com/phpBB3/viewtopic.php?f=28&t=1472&p=12317&hilit=numbers#p12317Now you might understand why one of my proudest Munster Irish moments was when I correctly asked for "the lids of these three saucepans" in Corca Dhuibhne.