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:23The fact that players with intermediating roles arise endogenously is in contrast with other models of intermediation, where intermediaries are exogenously assigned to their role, as for example in Rubinstein and Wolinsky (1987), and Blume et al. (2009).
Category: