The answers in (16b) and (18) giving an exhaustive listing reading are often distinguished as "restrictive focus", presupposing a set specified in discourse of which the constituent is a member (Erteschik-Shir 1997).
the present theory follows Steedman (2000aSteedman ( , 2000b in assuming that restrictive and nonrestrictive rhemes are semantically and grammatically indistinguishable, and only differ in the nature of the context in which they are uttered.