Distributional Point Values for Borel and Symmetric Borel Derivatives

Abstract

Borel and symmetric Borel derivatives are generalized derivatives defined through local averages of difference quotients. Distributional point values, in the sense of Łojasiewicz and its symmetric variants, are a classical way of describing the local value of a distribution. This paper connects these two ideas. Writing $T_f$ for the regular distribution generated by $f$, we prove that finite first and second symmetric Borel derivatives give symmetric distributional point values of $T_f'$ and $T_f''$, respectively. For the first symmetric derivative, Borel smoothness is used as a sufficient condition to pass from the symmetric point value to the full Łojasiewicz point value. We also prove that the one-sided Borel derivatives determine the right and left distributional point values of $T_f'$, and that the ordinary Borel derivative gives the full point value when the two one-sided averages agree. Examples show why the second-order symmetric result cannot be strengthened automatically.