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:Previous work has already shown that ssDNA-RecA filaments formed with ATP as the cofactor are much more flexible than filaments formed with ATP S as the cofactor (23–27) and that multiple separate sequence matched strand exchange products do form (20).
Category: