Wiki and mathworld only talk about C^r for functions of one variables, saying C^r is the space of function with and rth derivative that is continuous. But for a function of several variables to be C^r means that all its partial derivatives (mixed and not mixed) of order r are continuous, correct?(adsbygoogle = window.adsbygoogle || []).push({});

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# What does C^r mean for a function of several variables?

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