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 reduce indels at off-target sites, double nicking of opposite strands by the RuvC dead mutant Cas9D10A with two gRNAs has been proposed (Ran et al. 2013a; Shen et al. 2014).
Category: