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:The subsurface location C has essentially no elastic stress concentration but it has a residual tensile stress of about 0:4 Y. Fatigue cracks have been observed to nucleate at all three locations (Peters et al., 2002).
Category: