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:However, unlike Cochrane and Saa-Requejo (2000), the authors do not use a Sharpe ratio criterion to restrict the price interval for assets in incomplete markets, but a generalized version of the coherent risk measure first introduced by Artzner et al. (1999).
Category: