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Banach spaces, function spaces, real functions, integral transforms, theory of distributions, measure theory.

11 votes
1 answer
624 views

Inequivalent complete norms and the axiom of choice

Hi, I've been wondering about the following : Is it possible, without the axiom of choice, to have two inequivalent complete norms on a vector space? All the examples of inequivalent complete norms …
Malik Younsi's user avatar
  • 2,154
2 votes

$\mathcal P(K)=\mathcal R(K)$ iff $\Bbb C\backslash K$ is connected

Perhaps a more elementary proof is the following : Assume $\mathbb{C} \setminus K$ is disconnected. Let $V$ be a bounded component of $\mathbb{C} \setminus K$, and let $w \in V$. Let us show that the …
Malik Younsi's user avatar
  • 2,154
5 votes

In a Banach algebra, do ab and ba have almost the same exponential spectrum?

Bonjour Yemon, Oui, c'est un problème proposé par TJR dans le cadre d'un projet de recherche d'été CRSNG. It is indeed a very subtle question, I thought it might interest some people here. This probl …
Malik Younsi's user avatar
  • 2,154
7 votes

Reference for complex analysis jargon

I really recommend the book Potential Theory in the complex plane" by Thomas Ransford. It's a very nice book with exercises and it covers each of the 5 points you mentioned.
Malik Younsi's user avatar
  • 2,154
21 votes
2 answers
2k views

In a Banach algebra, do ab and ba have almost the same exponential spectrum?

Let $A$ be a complex Banach algebra with identity 1. Define the exponential spectrum $e(x)$ of an element $x\in A$ by $$e(x)= \{\lambda\in\mathbb{C}: x-\lambda1 \notin G_1(A)\},$$ where $G_1(A)$ is th …
Malik Younsi's user avatar
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