Accessibility is in the first instance a relation between DRSs; derivatively, it is also a relation between discourse referents. [6c1] is accessible to [6c2], but not the other way round, and therefore the discourse referents introduced in [6c1], i.e., x and z, are accessible from [6c2], but conversely, if we are in [6c1] we have no access to [6c2] and its discourse referents, i.e., y.  Thus in [6c] anaphora is not possible because y is not accessible to z. In [4a], by contrast, anaphora is possible, because x and y are accessible to v and w (the accessibility relation being reflexive). The notion of accessibility is crucial to DRT’s account of anaphora, and it is important to note that it is not stipulated, but is entailed by the semantics of the DRS language. [6c1] is accessible to [6c2] because every embedding function that must be considered for [6c2] is an extension of an embedding function for [6c1], and it is for this reason that every discourse referent in [6c1] is also defined in [6c2]. The converse, however, does not hold.