Continuity and the Riemann integrability criterion
A bounded real function on [a,b] is Riemann integrable exactly when its discontinuity set has Lebesgue measure zero.
Key knowledge
A bounded real function on [a,b] is Riemann integrable exactly when its discontinuity set has Lebesgue measure zero. In particular continuous functions and monotone functions on a compact interval are Riemann integrable.
Conditions and scope
- Finite a<b; continuity at endpoints is relative to the interval.
- Measure zero means that for every ε>0 a countable open-interval cover has total length below ε; it does not mean only finitely or countably many discontinuities.
Sources · 1
References
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Evidence and review
Theorems 11.28 and 11.30 with proofs, printed pages 219–220; Definition 11.59 and Theorem 11.61, printed pages 238–239. The general measure-zero criterion is stated here without a proof in this introductory source.
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