# Blacklist the [completeness] tag

Completeness is an important notion in mathematics. Metric spaces can be complete, a theory can be complete, a logic can be complete, and set of propositional connectives can be complete, and many other objects can be complete.

We tried to remove it already. But keeps coming back.

Maybe it's time to blacklist the tag entirely?

• Similar situations for duality-theorems. – user99914 Jul 18 '15 at 14:49
• I don't know much about duality theorems, but at least there it seems that there is some kind of unifying notion of duality. In the case of completeness, even if currently it's only been used on certain kind of completeness, the situation would be closed to [regularity] or [normality], where there's absolutely no way to understand the meaning of the tag. – Asaf Karagila Jul 18 '15 at 14:51
• Perhaps it's time to add tags like completeness - logic, completeness - metric spaces, etc. (I don't spend any time with tags so presumably there is a better/more consistent wording, but you get the idea) – Peter Woolfitt Jul 18 '15 at 15:12
• @Peter: Well, I don't think there's any need for the tags related to logic (not to mention that there are three types of completeness just when you come to talk about first-order logic, and they are all kinda different). Maybe if the guys who roam the category theory tags think it's useful, they can start one about various category related completeness. I also don't think that complete metric spaces deserve a separate tag. – Asaf Karagila Jul 18 '15 at 15:30
• @John: Amusingly, I ran into this old thing. :-) – Asaf Karagila Jul 30 '15 at 7:58
• @AsafKaragila : LOL!${}{}$ – user99914 Jul 30 '15 at 17:17

After a few reappearances following its initial removal, the tag is now blacklisted. This should probably help prevent its return.

• I should have told you that for completeness sakes, you should post this answer. I blame this missed opportunity on being tired. But Martin pointed you this way, which is also fine. – Asaf Karagila Sep 23 '15 at 12:22

Also, a measure space can be complete [meaning the subsets of null sets are measurable], a set of functions in a function space can be complete [meaning they span the space],... In addition to being ambiguous, this tag is also pretty far down on the hierarchy of usefulness.

From most to least useful:

1. Knowledge areas: , , ...
2. Mathematical objects: , , ...
3. Properties of mathematical objects: , , ...
4. Meaningless fluff: , , ...

Sure, let's blacklist . For now, I removed it from the questions that had it.

• I feel like I'm supposed to add tags to that list. – Asaf Karagila Jul 18 '15 at 16:49
• Saved you the trouble. – user147263 Jul 18 '15 at 16:51
• I would be tempted to add "Specific mathematical objects" between "Knowledge areas" and Mathematical objects". The main problem being that such tags aren't used very frequently. – user642796 Jul 18 '15 at 17:26
• @Arthur: Do you mean something like "this-set-right-here"? (Which is indeed not used very frequently, thank goodness.) – Asaf Karagila Jul 18 '15 at 17:29
• @AsafKaragila Perhaps more like the Banach–Mazur compactum. – user147263 Jul 18 '15 at 17:32
• I believe @Arthur means tags similar to (sorgenfrey-line) or (the-baire-space). See also this discussion in chat, which mentions sorgenfrey-line, and also discussion related to creating the-baire-space. – Martin Sleziak Jul 18 '15 at 17:42
• @Asaf: Thinking more like sorgenfrey-line, or klein-bottle, or constructible-universe (okay, the last one has the unfortunate defect of not actually existing). Not every question is about a specific, named mathematical object, but those that are benefit, IMHO, by being so categorised, for easier dupe-searches if nothing else. – user642796 Jul 18 '15 at 17:42
• @Arthur: If the tag has returned in the meantime, is this casus belli to have it blacklisted? – Asaf Karagila Jul 30 '15 at 17:38
• @Arthur: It's keep coming back! – Asaf Karagila Sep 22 '15 at 22:51