12:32 AM
Only now I noticed that Glorfindel created also tag-excerpt for .
> This is a special tag that is designed to be used only by the system for questions that have had all of their other tags removed. Do not add this tag to existing questions, it is reserved for use by the system to identify posts with no valid tags.
At the moment, there is exactly one questions with this tag:
1

My question is the following: if I know $f''(x)<0,~\forall~0\leq x\leq a$ and I know that $f'(c)=0$ where $c\in[0,a]$ and I also know $f(0)=0$, then is that true $f(x)>0,~\forall~x\in(0,c]$? I think it is correct.

This tag cannot be added by regular users, only by system. (For example, if a tag with single occurrence is removed, or if a question is migrated here from another site by moderators and none of the original tags exist on this site.)

12:49 AM
As mentioned before, the above question originally had tag. (And it was eventually removed by the system - since it was used on a single question and had empty tag-wiki.)

7 hours later…
7:33 AM
Proofs shown to be wrong after formalization with proof assistant I have added . Would also be a good tag for this question? It does not have top-level tag - should be used here?