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:(1999) and modified by Grant and Bogdanowicz (2006). Enrichment of the library was with the same set of dimeric, trimeric and tetrameric oligonucleotide repeats as Barnett et al.
Category: