What is the relationship between boundedness, total boundedness and compactness in topological vector space?

62 Views Asked by At

In our lecture notes, we have that in a topological vector spaces, every compact set is totally bounded and every totally bounded set is bounded but is the converse true?

1

There are 1 best solutions below

0
On

None of the two implications reverse even in the small class of Banach spaces. (small compared to all TVS's I mean).

Any open ball in $\Bbb R^n$ is totally bounded but not compact.

The closed unit disk $D_1:=\{x\mid \|x\|_\infty\le 1\}$ in $\ell^\infty$ (in ts sup norm $\|\cdot\|_\infty$) is bounded (norm-bounded implies TVS-bounded) but not totally bounded (or $D_1$ would be compact which it is not).