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:Inasmuch as glutamate was found to be an extremely poor substrate for the neutral/basic amino acid symporter (Hennigan et al. 1993a) or any other symporter characterized to date in M. sexta, an evaluation of glutamate uptake under alkaline conditions seemed important.
Category: