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:…(GA; Serifoglu and Ulusoy, 2004; Oguz and Ercan, 2005; Engin et al, 2011), ant colony optimization (ACO; Ying and Lin, 2006), iterated greedy (IG; Ying, 2009), particle swarm optimization (PSO; Tseng and Liao, 2008; Chou, 2013), artificial bee colony (ABC; Lin et al, 2013a), shuffled…
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