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:In addition, the rows in the stoichiometric matrix M corresponding to the mass balances of the dependent enzyme states can be eliminated so that a new, reduced, stoichiometric matrix MR is formed (Heinrich and Schuster, 1996; Reder, 1988).
Category: