In Italian, the values singular, plural, and invariant, i.e.
the same morphological form for the singular and the plural are used.
This last value can be seen as a multilabel whose semantics
is a ``disjunction" operation:
in fact, the value n is a macro for sg 
pl.
It is used for the lexicon encoding of
the series of the invariant nouns.
For these nouns,
the number can be decided in the context only on the basis of syntactic
considerations, i.e. by observing the agreement with other elements,
articles, verbs, adjectives:
Parigi e' una citta' europea; le citta' europee hanno alcune
caratteristiche in comune.
Sometimes the number can remain undecided, notwithstanding the context,
i.e. when the noun agrees with
invariant adjectives:
sarebbe opportuno offrire pari opportunita' (sing. or plur.?).