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 existence of bona fide human naive pluripotent stem cells remains controversial, although various methods have been reported for maintaining hPSCs in states similar to those of mESCs (Hanna et al., 2010; Gafni et al., 2013; Chan et al., 2013; Takashima et al., 2014; Theunissen et al., 2014; Valamehr et al., 2014; Wang et al., 2014; Ware et al., 2014; Chen et al., 2015; Duggal et al., 2015; Hayashi et al., 2015; Qin et al., 2016).
Category: