"Bha mi a' sgrìobhadh leabhar ann an leabharlann."
Translation:I was writing a book in a library.
In the Tips and Notes section (https://www.duome.eu/tips/en/gd), it says that "ann an" and "ann am" are to be considered as meaning just "in a". Here's the note: Although ann an and ann am resemble the definite masculine articles an and am, we only use them before indefinite nouns (words without "the" before them). We teach how to say "in the" later in the course."
If it is apparent to both speakers which library is being refered to, would you say 'anns an' or would it still be 'ann an'?
I know it's "bha mi ag an t-oilthigh an duigh" in gaelic, even though it's just 'at university' in english. Is this one of those cases where the languages use the articles differently?