Assume that a given question has several answers.

So in the answer part there are 3 button "Active", "Oldest" and "Vote"

I doubt that the answer to this meta question is affirmative since it does not work for example on this question

Finding a 1-form adapted to a smooth flow

On the other hand the situation is different for the following question with several answers

If $x_{n+1}= \frac{nx_{n}^2+1}{n+1}$ then $x_{n}=1$

So what does "oldest" signify?

oldest does sort by the answer time, however, the accepted answer will still be on top, even if it is not the oldest; the same applies to the other sort options.

• Thank you for your answer. – Ali Taghavi Aug 15 '17 at 13:05