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:In this chapter we will present the formalism for these different kinds of beamformers in their scalar form, then develop the formalism for a vector beamformer (Sekihara et al., 2001, Quraan and Cheyne 2010) and an eigenstate-projected vector beamformer (Sekihara et al., 2001).
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