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:On the other hand, whilemuch of the research in this direction is focused on understanding the data geometry, the theoretical foundations for the problems of function approximation and harmonic analysis on such data-defined manifold are developed extensively inMaggioni andMhaskar [8], Filbir andMhaskar [42, 43], Mhaskar [44, 45] and Chui and Mhaskar [46].
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