12. Banach spaces (Sir Michael Atiyah, from http://www.johndcook. com/blog/2013/09/24/interview-with-sir-michael-atiyah/.)
![functional analysis - Proof that a linear map T is bounded if and only if the inverse image of the unit ball has nonempty interior - Mathematics Stack Exchange functional analysis - Proof that a linear map T is bounded if and only if the inverse image of the unit ball has nonempty interior - Mathematics Stack Exchange](https://i.stack.imgur.com/wGB7E.png)
functional analysis - Proof that a linear map T is bounded if and only if the inverse image of the unit ball has nonempty interior - Mathematics Stack Exchange
![reference request - Is $(\ell^1(\mathbb N_0),\sigma(\ell^1,\ell^\infty))$ not quasi-complete? - MathOverflow reference request - Is $(\ell^1(\mathbb N_0),\sigma(\ell^1,\ell^\infty))$ not quasi-complete? - MathOverflow](https://i.stack.imgur.com/opjJK.png)