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:method developed in [6,8] and improved in [10,18], where we first discretize in space, using a Finite Difference scheme, then discretize in time, using an implicit multistep scheme, of the BDF family (Backward Differentiation Formula).
Category: