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:4: we use a concatenation
of 16-bin histograms as in (Gray and Tao, 2008; Prosser et al., 2010; Zheng et al., 2011) (see also Fig.
Category: