Consider a proof that reads:
By theorem 2.1 and lemma 3.5 we get equation 8 and hence the result.If the above looks abstruse in print, it sounds meaningless in audio. This is a serious drawback when listening to mathematical books on cassette, where it is practically impossible to locate the cross-reference. AsTeR is more effective, since these cross-reference links can be traversed, but traversing each link while listening to a complex proof can be distracting.
Typically, we only glance back at cross-references to get sufficient information to recognize theorem 2.1. AsTeR provides a convenient mechanism for building in such information into the renderings. When rendering a cross-referenceable object such as an equation, AsTeR verbalizes an automatically generated label (e.g., the equation number) and then generates an audible prompt. By pressing a key at this prompt, a more meaningful label can be specified, which will be used in preference to the system-generated label when rendering cross-references.
To continue the current example, when listening to theorem 2.1, suppose the user specifies the label ``Fermat's theorem''. Then the proof shown earlier would be spoken as:
By Fermat's theorem and lemma 3.5 we get equation 8 and hence the result.Of course, the user could have specified labels for the other cross-referenced objects as well, in which case the rendering produced almost obviates the need to look back at the cross-references.