# Is compact operator weak-to-norm continuous?

1. Can we say a compact operator is weak-to-norm continuous?
2. What do we say about converse of question 1?
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Is the underlying space a Banach space or a Hilbert space? –  J. Loreaux Aug 3 '12 at 22:28

@t.b. That's right. I was reading some paper on $C^*$-algebras so I had a Hilbert space on my mind. I'll leave the answer in case the OP was about reflexive spaces. –  azarel Aug 3 '12 at 22:31
For part 2., more can be said: If $T:X\rightarrow Y$ is weak-to-norm continuous where $X$ and $Y$ are Banach spaces, then $T$ has finite rank. One can prove this using an argument similar to those in this post and this post (Use the fact that the inverse image under $T$ of the unit ball of $Y$ is weakly open to find $f_1,\ldots,f_n$ in $X^*$ so that $\Vert Tx\Vert\le 1$ whenever $|x_i^*x|<1$ for all $i$. Then show that the kernal of $T$ must contain the subspace $\cap_{i=1}^n \text{ker}( f_i)$ of $X$. This subspace has codimension at most $n$; thus $T$ has rank at most $n$).