Tagging - 2020-08-05

12:16 PM

specific-post I would be tempted to add separation-axioms here, but all 5 spots are already used: “Naturally occurring” non-Hausdorff spaces?

39

Q: "Naturally occurring" non-Hausdorff spaces?

It is not difficult for a beginning point-set topology student to cook up an example of a non-Hausdorff space; perhaps the simplest example is the line with two origins. It is impossible to separate the two origins with disjoint open sets. It is also easy for a beginning algebraic geometry studen...

Xander Henderson

1:34 PM

@MartinSleziak the complex-analysis tag seems unnecessary on that post. Perhaps replace it?

user185131

2:05 PM

@XanderHenderson Seconded

Martin Sleziak

2:38 PM

40

Q: "Naturally occurring" non-Hausdorff spaces?

It is not difficult for a beginning point-set topology student to cook up an example of a non-Hausdorff space; perhaps the simplest example is the line with two origins. It is impossible to separate the two origins with disjoint open sets. It is also easy for a beginning algebraic geometry studen...

general-topology algebraic-geometry examples-counterexamples big-list separation-axioms

Xander Henderson

@MartinSleziak Thumbs up emoji.

Eric

4:48 PM

@MartinSleziak @XanderHenderson I'm inclined to rollback. My question isn't really about the specific separation axioms, it's instead looking for examples from a wide range of mathematics. Taking away the complex-analysis tag, to me, makes it appear like I'm only looking for geometric examples: [general-topology] and [algebraic-geometry]. But in fact I want to see more analysis examples, since it's outside my domain and I would like to learn of these. Thoughts?

Martin Sleziak

@Eric As the question is about Hausdorff condition, I still think that it is suitable to have tags which reflect that. But that's just my opinion.

It's your call - at least, to some extent - after all it's your question.

Eric

@MartinSleziak Thank you! I will go ahead and rollback.

Xander Henderson

5:15 PM

@Eric If you are interested in examples in analysis, it might be better to actually write that into the question. As it currently stands, it is not at all clear why the question should be tagged complex-analysis. As stated, the question is more about the separation axioms (i.e. Hausdorffiness) than it is about complex analysis, or algebraic geometry.

Of course, it's your question.

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$Mathematics$ Tagging