And yet more questions from me;
Here we have "leabharlainne" which looks like the nominative plural, but given that we're doing a lesson on the tuiseal ginideach I am guessing that it is in fact the genitive singular in this sentence.
If this is the case, they why is the English not "a library's book" ? That is, why is "library" used like an adjective (to describe the book), as opposed to being the possessor (to own the book)?
How is it redundant? Do you mean because the two words sound simailar? And how would one shorten it?
The nearest thing I can think of to illustrate the question in English is 'the bookshop's book.' You might use it in a sentence like 'The bookshop's book about Irish grammar.' I can't think of a way to shorten that. Or in French maybe 'la Bible de la bibliotheque' as in 'the library's Bible.' (sorry, I can't get that French accent which looks like a backward fada over the first 'e'.) There is no way to change those sentences in either language without subtly changing the meaning of the sentence. And in each case they are grammatically correct.
(I hope the above doesn't sound too pompous - I hate that the internet makes discussion appear dry. I honestly am not trying to be a git here, I really am trying to work through nuances, and this is an interesting question.)
declension 2 f (except im, teach and slaibh) gs. palatalisation + -e
ns. leabharlann gs. leabharlainne, npl. leabharlanna [strong because no palatisation like gs. and ending in -anna?].
For gpl. teanglann shows only a squiggle. That, in dictionaries, normally means it's equivalent to the main entry, which would here mean that gpl. = ns, that is gpl. leabharlann But that's only the case for weak plurals :(
Who can confirm npl. and gpl. of leabharlann, or knows where teanglann.ie is hiding it's dictionary preface that explains its unconventional notation?
The nominative singular is leabharlann, the nominative plural is leabharlanna - that is a weak plural.
The preface for the FGB is written in Irish.
The third page has a section entitled Comhartaí that includes this line:
~ ag seasamh don cheannfhocal slán agus é á athlua san alt mínithe
(standing for the intact headword when it is repeated in the explanatory paragraph).
If you want an explanation in English, have a look at that the "Look inside" selection for the book "A Learners Guide to Irish" on Amazon. The "Look Inside" includes a section on "The Ó Dónaill Dictionary" (aka FGB) that explains the key symbols used in the dictionary.