ガロア第一論文と乗数イデアル他関連資料スレ6

１３２人目の素数さん

>>283
>>その測度が0でない場合は区分をいくら小さくしても上積分と下積分の差が0に収束させることができない
>これは測度の定義からすぐ出せますか？

カンニングですが、下記ですね
（>>266より再録）

https://en.wikipedia.org/wiki/Riemann_integral
Riemann integral
Integrability
A bounded function on a compact interval [a, b] is Riemann integrable if and only if it is continuous almost everywhere (the set of its points of discontinuity has measure zero, in the sense of Lebesgue measure). This is the Lebesgue-Vitali theorem (of characterization of the Riemann integrable functions). It has been proven independently by Giuseppe Vitali and by Henri Lebesgue in 1907, and uses the notion of measure zero, but makes use of neither Lebesgue's general measure or integral.

The integrability condition can be proven in various ways,[4][5][6][7] one of which is sketched below.

Proof
The proof is easiest using the Darboux integral definition of integrability (formally, the Riemann condition for integrability) – a function is Riemann integrable if and only if the upper and lower sums can be made arbitrarily close by choosing an appropriate partition.

One direction can be proven using the oscillation definition of continuity:[8] For every positive ε, Let Xε be the set of points in [a, b] with oscillation of at least ε. Since every point where f is discontinuous has a positive oscillation and vice versa, the set of points in [a, b], where f is discontinuous is equal to the union over {X1/n} for all natural numbers n.

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