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:, 1993), and the nuclear mitotic apparatus (NuMA) proteins (Lydersen and Pettijohn, 1980; Compton et al., 1992; Yang and Snyder, 1992).
Category: