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:Because ribbons and short-wavelength folds occur together at the margins of crustal plateaus and show compatible principal strain orientations [Ghent and Hansen, 1999], it is possible that they formed simultaneously, under the principle that the shortest-wavelength tectonic features represent the earliest stages of deformation.
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