What is the condition for a function to be integrable with improper integral?

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The discussion centers on the conditions under which a function can be considered integrable despite being undefined at certain points. For Riemann integrals, a function can be integrable if it is undefined at a countable number of points, provided these points are not dense in any interval (a, b) of R. In contrast, for Lebesgue integrals, a function can remain integrable even if it is undefined on an uncountable subset, as long as the undefined points form a set of measure zero or are contained within a measurable set of measure zero.

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LHeiner
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Hello

i stumbled over a question and I'm not sure how to proof/ solve hat:

At how many points a function can not be defined to be nevertheless integrable (improper integral)?

Thx in advance!
 
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If you are talking about Riemann integral, a countable number of points. However in many cases there could be a problem, since the set of rationals is countable.

For Lebesgue integral, a set of measure 0. This is a much better criterion.
 
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Interestingly for lebesgue integrals a function can be left undefined on an uncountable subset of R and still be integrable.

An even weaker condition is weaker for lebesgue integrals though, the set need only be a subset of a measurable set of measure 0.

For riemann integrals I think it is sufficient that the countable set of points where the function is undefined is not dense in any interval (a,b) of R.
 

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