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 perform a time calibrated phylogenetic analysis, using three node constraints derived from Santos et al. (2009) in the software Beast 1.7 (Drummond and Rambaut 2007): (1) the divergence between Dendrobates truncatus and Dendrobates auratus was constrained with an uniform prior with an…
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