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:Digynic triploidy may also develop after fertilization of a diploid giant oocyte (Dyban and Baranov, 1987) but this has been considered rather improbable (Jacobs et al., 1978; Kaufman, 1991).
Category: