Return to Revisions

Tim: here's one from a course I am giving now (I think you know which): let $B\subset \mathbb{R}^n$ be a nonempty subset. Then there is a norm on $\mathbb{R}^n$ whose open unit ball is $B$ iff $B$ is open, convex, symmetric and bounded. (I think it would be poor style to move "nonempty" into the 2nd sentence, since that is such an obvious condition, but that would make 5...)