[5b2] contains a token of the discourse referent x which is introduced externally, in the DRS in which [5b2] is embedded, i.e., [5b1]. Apart from that, [5b2] also introduces a discourse referent of its own, i.e., y, which is associated with the indefinite NP “a donkey”, and whose scope is delimited by [5b2]. Consequently, it doesn’t make sense to refer to y outside of [5b2]. In DRT, this is taken to explain why the “lifespan” of the individual introduced by the indefinite NP in [5a] is delimited by the scope of the negation operator. If [5a] were followed by [6a], for example, the pronoun could not be linked to the indefinite: