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:Then, to transfer knowledge, one can either share the S(k) = {U ,V } (Pan et al., 2010) or S(k) = B (Gao et al., 2013b;a; Li et al., 2009; Long et al., 2012) across all domains.
Category: