This is just a quick question about sets that include plus or minus infinity on the extended real line. I am wondering about this in regards to measure in analysis so specifically, is [-∞,a) open or closed? I hadn't seen the extended reals before this class and we really didn't spend anytime discussing them. I want to say it is open since it certainly does not have a boundary point on the a) side and it seems like there isn't anything to approach the boundary on the [-∞. Moreover, it's complement [a,∞] looks suspiciously like a closed set.... Any verification on these musings? Thanks(adsbygoogle = window.adsbygoogle || []).push({});

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# Closed or open question about the Extended Real line

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