Complex homomorphisms on self-conjugate algebras of functions

Complex homomorphisms on self-conjugate algebras of functions Let X be a non-void set and A be a subalgebra of $${\mathbb{C}^{X}}$$ . We call a $${\mathbb{C}}$$ -linear functional $${\varphi}$$ on A a 1-evaluation if $${\varphi(f) \in f(X) }$$ for all $${f\in A}$$ . From the classical Gleason–Kahane–Żelazko theorem, it follows that if X in addition is a compact Hausdorff space then a mapping $${\varphi}$$ of $${C_{\mathbb{C}}(X) }$$ into $${\mathbb{C}}$$ is a 1-evaluation if and only if $${\varphi}$$ is a $${\mathbb{C}}$$ -homomorphism. In this paper, we aim to investigate the extent to which this equivalence between 1-evaluations and $${\mathbb{C}}$$ -homomorphisms can be generalized to a wider class of self-conjugate subalgebras of $${\mathbb{C}^{X}}$$ . In this regards, we prove that a $${\mathbb{C}}$$ -linear functional on a self-conjugate subalgebra A of $${\mathbb{C}^{X}}$$ is a positive $${\mathbb{C}}$$ -homomorphism if and only if $${\varphi}$$ is a $${\overline{1}}$$ -evaluation, that is, $${\varphi(f) \in\overline{f\left(X\right)}}$$ for all $${f\in A}$$ . As consequences of our general study, we prove that 1-evaluations and $${\mathbb{C}}$$ -homomorphisms on $${C_{\mathbb{C}}\left( X\right)}$$ coincide for any topological space X and we get a new characterization of realcompact topological spaces. Positivity Springer Journals

Complex homomorphisms on self-conjugate algebras of functions

Loading next page...
SP Birkhäuser Verlag Basel
Copyright © 2010 by Springer Basel AG
Mathematics; Econometrics; Calculus of Variations and Optimal Control; Optimization; Potential Theory; Operator Theory; Fourier Analysis
Publisher site
See Article on Publisher Site


You’re reading a free preview. Subscribe to read the entire article.

DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 12 million articles from more than
10,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Unlimited reading

Read as many articles as you need. Full articles with original layout, charts and figures. Read online, from anywhere.

Stay up to date

Keep up with your field with Personalized Recommendations and Follow Journals to get automatic updates.

Organize your research

It’s easy to organize your research with our built-in tools.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

Monthly Plan

  • Read unlimited articles
  • Personalized recommendations
  • No expiration
  • Print 20 pages per month
  • 20% off on PDF purchases
  • Organize your research
  • Get updates on your journals and topic searches


Start Free Trial

14-day Free Trial

Best Deal — 39% off

Annual Plan

  • All the features of the Professional Plan, but for 39% off!
  • Billed annually
  • No expiration
  • For the normal price of 10 articles elsewhere, you get one full year of unlimited access to articles.



billed annually
Start Free Trial

14-day Free Trial