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Example of a Monotonic, Everywhere Differentiable Function on ℝ Whose Derivative Is not Continuous

https://doi.org/10.4169/amer.math.monthly.120.06.566 https://www.jstor.org/stable/10.4169/amer.math.monthly.120.06.566 Abstract We construct an example of a monotonic ...
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On the Strong Unicity of Best Chebyshev Approximation of Differentiable Functions

Let X be a normed linear space, Un an n-dimensional Chebyshev subspace of X. For f ∈ X denote by p(f) ∈ Un its best approximation in Un. The problem of strong unicity consists in estimating how fast ...