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:…independent real factor analysis (or noisy ICA), together with the corresponding criteria for the number of independent factors (Xu, 1998b, 2000, 2001a); as well as (e) several extensions of LMSER learning and the corresponding criteria for the number of hidden units (Xu, 1993, 1998b, 2000, 2001a).
Category: