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2. Cannon, J. R., Miller, Keith: Bounds for the ratio between the fit of interpolation and the best fit. (1964) Unpublished.
3. Cheney, E. W.: Introduction to approximation theory. New York-London: McGraw-Hill Book Co. 1967.
4. Davis, P. J.: Interpolation and approximation. (2nd Edition.) New York-London: Blaisdell Pub. Co. 1965.
5. Guerra, S.: Osservazioni su un noto teorema di Jackson. Boll. Un. Mat. Ital. (3)18, 57–64 (1963) (Translation by Pauline Radcliffe, University of Manchester.)