Adjectives agree in number to the nouns which they specify.
In Italian, the values singular, plural, and
invariant, i.e. the same morphological form for
the singular and the plural are pertinent to adjectives.
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 so-called invariant adjectives.
For these adjectives,
the number can be decided in the context only on the basis of syntactic
considerations, i.e. by observing the number of the agreed noun:
e' tornata una somma pari.
Sometimes the number can remain undecided, notwithstanding the context,
i.e. when the adjective agrees with common nouns: in
pari opportunita', che non sempre a tutti vengono offerte
the number could be decided only by a parsing of
the sentence.