The structure of ideals, point derivations, amenability and weak amenability of extended Lipschitz algebras

Abstract

Let $(X,d)$ be a compactmetric space and let $K$ be a nonempty compact subset of $X$. Let $alpha in (0, 1]$ and let ${rm Lip}(X,K,d^ alpha)$ denote the Banach algebra of all continuous complex-valued functions $f$ on$X$ for which$$p_{(K,d^alpha)}(f)=sup{frac{|f(x)-f(y)|}{d^alpha(x,y)} : x,yin K , xneq y}<infty$$when it is equipped with the algebra norm $||f||_{{rm Lip}(X, K, d^ {alpha})}= ||f||_X+ p_{(K,d^{alpha})}(f)$, where $||f||_X=sup{|f(x)|:~xin X }$. In this paper we first study the structure of certain ideals of ${rm Lip}(X,K,d^alpha)$. Next we show that if $K$ is infinite and ${rm int}(K)$ contains a limit point of $K$ then ${rm Lip}(X,K,d^alpha)$ has at least a nonzero continuous point derivation and applying this fact we prove that ${rm Lip}(X,K,d^alpha)$ is not weakly amenable and amenable.