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:Supplementary motor area was defined as cortex on the medial wall forward of the precentral sulcus, superior to the cingulate sulcus (or the paracingulate sulcus, when present), and behind the coronal plane perpendicular to the anterior commissure – posterior commissure (AC – PC) line and tangent to the posterior margin of the AC (Chainay et al. 2004; Fink et al. 1997).
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