Continuity of discrete homomorphisms of diffeomorphism groups

Homomorphisms between Diffeomorphism Groups

For r ≥ 3, p ≥ 2, we classify all actions of the groups Diffc(R) and Diff+(S) by Cdiffeomorphisms on the line and on the circle. This is the same as describing all nontrivial group homomorphisms between groups of compactly supported diffeomorphisms on 1-manifolds. We show that all such actions have an elementary form, which we call topologically diagonal. As an application, we answer a question...

Separate and Joint Continuity of Homomorphisms Defined on Topological Groups

In this paper we prove the following theorem. “Let H be a countably Čech–complete topological group, X be a topological space and (G, ·, τ) be a topological group. If f : H ×X → G is a separately continuous mapping with the property that for each x ∈ X, the mapping h 7→ f(h, x) is a group homomorphism, then for each q–point x0 ∈ X the mapping f is jointly continuous at each point of H ×{x0}.” W...

Automatic continuity of group homomorphisms

We survey various aspects of the problem of automatic continuity of homomorphisms between Polish groups.

Automatic continuity of surjective $n$-homomorphisms on Banach algebras

In this paper, we show that every surjective $n$-homomorphism ($n$-anti-homomorphism) from a Banach algebra $A$ into a semisimple Banach algebra $B$ is continuous.

Automatic Continuity of Homomorphisms Between Banach algebras and Frechet algebras