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:Since in the worst case a k-safe hypercube network Hn can tolerate no more than 2 (n−k)−1 faulty nodes [17, 35], this line of research still assumes a bound O(n) on the number of faulty nodes in Hn.
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