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Let $X$ be a Banach space. Consider the modulus of convexity and the characteristic of convexity $\epsilon_0$. Is the modulus of convexity strictly monotonically increasing in the interval $[\epsilon_0, 2]$.

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    $\begingroup$ no idea. what have you tried? $\endgroup$
    – Will Jagy
    Commented Mar 21, 2013 at 5:06

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Yes. $\delta(\epsilon)/\epsilon$ is nondecreasing on $[0,2]$, so once $\delta(\epsilon)$ is nonzero it is strictly increasing. See T. Figiel, On the moduli of convexity and smoothness, Studia Math. 56 (1976), 121–155.

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