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:Although they mimic many phorbol ester effects, including inhibition of cell-cell communication (25, 26), they have been reported not to induce differentiation of HL-60 cells (27) or to inhibit maturation of granulosa cells (28).
Category: