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 first-round PCR products were used directly in a second round of PCR using primers 2B and F (Hatada et al., 2010; Shibata et al., 2007; Yoshimura et al., 2006, 2010b) for gp120, IN 2F (59-CTGGCATGGGTACCAGCACACAA-39) and IN 2R (39-CCTAGTGGGATGTGTACTTCTGAACTTA-39) for IN, and IN 2F and F for…
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