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:To finish, it is worth mentioning that in [12, 13] it has been shown that both the Jonesmatrix formalism and the Stokes parameters in polarization optics can be reformulated as two different representations of the same Lorentz group.
Category: