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:Although a back-reaction from hL to hKL was not explicitly included in the model, it was noted that such a reaction could contribute to the long-lived HOOP modes (Dioumaev and Braiman, 1997a).
Category: