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:Two distinct steps define mitochondrial division - an initial constriction of mitochondrial membranes, followed by final membrane scission (Friedman et al., 2011; Korobova et al., 2013;Murley et al., 2013; Korobova et al., 2014).
Category: