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:The definition we used for prolonged postoperative ileus followed the recommendations published by Vather et al. (2013): the absence of passage of flatus/stool or inability to tolerate oral diet ‚â• 4 postoperative days.
Category: