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:Increasing evidence indicates that penetration of the SFV genome into a cell involves membrane fusion and that the most likely site for penetration is the secondary lysosome (Helenius et al., 1980a, b; White & Helenius, 1980; White et al., 1980, 1981).
Category: