"The boy eats both sweets and vegetables."
Translation:Itheann an buachaill idir mhilseáin agus ghlasraí.
Bit of a necro post I realize, but in the above link it says, among other things:
pairings: both... and (with agus), (use of the singular): idir fhear agus bhean = men and women, idir balla agus ceann = walls and roof, idir sean agus óg = young and old,
It's not obvious to me why it's idir fhear agus bhean but it's idir balla agus ceann. I mean, both balla and ceann are leniteable, so why aren't they lenited in this case while fhear and bhean are?
I am inclined to interpret “no lenition if distance, time, difference or opposition is being expressed” in a much broader sense than it seems to have at first: I too thought that those concepts had to be expressed by idir alone, but it seems that if they apply to the general meaning of the sentence they can affect the lenition in that specific place. So, even though men and women are opposites, the general meaning of the sentence is not opposition between them, but rather sharing something, while walls and roof or young and old may be treated mire like opposites in real life situations? There’s no way of being sure when you have no context at all, not even the rest of the sentence.
Occam's Razor suggests that the simplest explanation is that there's an error in that page of Gramadach na Gaeilge. That entry also says that idir sean agus óg = "young and old", but the FGB says that it is idir shean agus óg (and the FGB gets the order right in the translation).
idir balla agus ceann actually means "between walls and roof".