supremum equals to infumum The question is:
What can you say about the set M if sup M = inf M.
I know that supremum is the lowest upper bound and infumum is the biggest lower bound. But I cant figure out what you can say about the set M. And we only had one lession about supremum and infumum.

Hint: Assume $a,b\in M$ with $a<b$. What can you say about $\inf M$ compared to $a$? What about $\sup M $ compared to $b$? What does that tell about $\inf M$ compared to $\sup M$?
