Banach Function Algebras of n-Times Continuously Differentiable Functions on R^d Vanishing at Infinity and Their BSE-Extensions

J. Korean Math. Soc. Published online 2019 Apr 10

Jyunji Inoue, and Sin_Ei Takahasi
Hokkaido University, Yamagata University

Abstract : In authors' paper in 2007, it was shown that the BSE-extension of $C^1_0(\mathbf{R})$, the algebra of continuously differentiable functions $f$ on the real number space $\mathbf{R}$ such that $f$ and $df/dx$ vanish at infinity, is the Lipschitz algebra $Lip_1(\mathbf{R})$.
This paper extends this result to the case of $C^n_0(\mathbf{R}^d)$ and $C^{n-1,1}_b(\mathbf{R}^d)$, where $n$ and $d$ represent arbitrary natural numbers. Here $C^n_0(\mathbf{R}^d)$ is the space of all $n$-times continuously differentiable functions $f$ on $\mathbf{R}^d$ whose $k$-times derivatives are vanishing at infinity for $k=0,...,n$, and $C^{n-1,1}_b(\mathbf{R}^d)$ is the space of all $(n-1)$-times continuously differentiable functions on $\mathbf{R}^d$
whose $k$-times derivatives are bounded for $k=0,...,n-1$, and $(n-1)$-times derivatives are Lipschitz. As a byproduct of our investigation we obtain an important result that $C^{n-1,1}_b(\mathbf{R}^d)$ has a predual.