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:To analyze the stability of such a multi-agent system, there are many possible approaches, such as the frequency domain approach (Olfati-Saber & Murray, 2004), the Lyapunov-based approach (Chopra & Spong, 2006; Hong et al., 2008; Lin et al., 2008; Liu & Passino, 2006; Olfati-Saber & Murray, 2004;…
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