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Published online by Cambridge University Press: 24 October 2008
Ryll-Nardzewski has proposed the following problem (New Scottish Book, no. 119). If fn(x) are continuous, differentiable* functions in a closed finite interval, do there always exist constants cn (no cn = 0) (depending on the ), such that converges and is also a continuous differentiable function?
* Throughout this article,‘differentiable’ means:‘with a finite (two-sided) derivative at every point’; this derivative may be unbounded. Thus is diffierentiable at x = 0; yẏ=⅓ is not.Google Scholar
† We shall assume this condition implicitly in all the work that follows.Google Scholar
‡ More generally, would also display all the relevant phenomena.Google Scholar
§ A's are absolute constants. O(1), o(l) refer to K →∞.Google Scholar