Locally integrable function

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at a point $M$

A function that is integrable in some sense or other in a neighbourhood of $M$. If a real-valued function $f$, defined on the interval $[a,b]$, is the pointwise finite derivative of a function $F$, real-valued and defined on this interval, then $f$ is locally Lebesgue integrable at the points of an open everywhere-dense set on $[a,b]$. In the two-dimensional case (see [2]) there is a real-valued function $f$, defined on the square $[0,1]\times[0,1]$, that is the pointwise finite mixed derivative in either order $\partial^2F/\partial x\partial y=\partial^2F/\partial y\partial x=f(x,y)$ and that is not locally Lebesgue integrable at any point of the square.


[1] S. Saks, "Theory of the integral" , Hafner (1952) (Translated from French)
[2] G.P. Tolstov, "On the curvilinear and iterated integral" Trudy Mat. Inst. Steklov. , 35 (1950) pp. 1–101 (In Russian)
How to Cite This Entry:
Locally integrable function. Encyclopedia of Mathematics. URL:
This article was adapted from an original article by I.A. Vinogradova (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article