{li abu} is another use
for the letter "a", this time not as a pronoun but as
the value of a variable, although I'm not very clear
what type of variable this is supposed to be and how
it is different from a pronoun.
It is not different at the level of predicate logic.
By convention, its referent is taken to be a mathematical
object. It is also syntactically different: "ko'a le mlatu" is two
sumti, even if the current referent of "ko'a" is a number,
whereas "ny. le mlatu" is a single sumti meaning "N of
the cats I have in mind".