# continuity – Is it possible to define integration over a discontinous domain?

I’m trying to think about this from the Riemannian integration perspective so let me know if Lebesgue integration or something else is better. An example where I seem to be running into problems is with integration over the domain $$mathbb{R}setminusmathbb{I}$$. If you want to integrate $$fcolonmathbb{R}rightarrowmathbb{R}setminusmathbb{I}$$ given by

$$begin{equation} f(x) = e^{-x} end{equation}$$

over $$D = (0, 4)$$, you should be able to get away with Riemannian integration (even though the interval is discontinuous) since the discontinuities are negligible. I guess my intuition for this is that $$f(x)Delta{x}$$ will disappear in the limit $$Delta{x}rightarrow0$$ for these discontinuities since they are finite. In a Riemannian sum, as the number of partitions goes to infinity, the contributions (or lack thereof) of 4 pieces will make no difference. So in that sense this integral over a finite domain seems to make sense, or be something we can in a way “get away with”. But what about the integral from $$0$$ to $$infty$$? In that, we have an infinite number of missing partitions. What would the difference amount to? How do you compute or even define integration here?

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