Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Particularly, when A‘ ¼ 0 it reduces into the normalized RBF nets (Moody & Darken, 1989; Nowlan, 1990; Xu, 1998a; Xu et al., 1994).
Category: