Acta Mathematica Scientia ( IF 1.2 ) Pub Date : 2021-01-29 , DOI: 10.1007/s10473-021-0210-5 Shaoqiang Shang
In this paper, we prove that (X, p) is separable if and only if there exists a w*-lower semicontinuous norm sequence \(\left\{ {{p_n}} \right\}_{n = 1}^\infty \) of (X*, p) such that (1) there exists a dense subset Gn of X* such that pn is Gâteaux differentiable on Gn and dpn (Gn) ⊂ X for all n ∊ N; (2) pn ≤ p and pn → p uniformly on each bounded subset of X*; (3) for any α ∈ (0, 1), there exists a ball-covering \(\left\{ {B\left( {x_{i,n}^*,{r_{i,n}}} \right)} \right\}_{i = 1}^\infty \) of (X*, pn) such that it is α-off the origin and x *i, n ∈ Gn. Moreover, we also prove that if Xi is a Gâteaux differentiability space, then there exist a real number α > 0 and a ball-covering \(\mathfrak{B}_i\) of Xi such that \(\mathfrak{B}_i\) is α-off the origin if and only if there exist a real number α > 0 and a ball-covering \(\mathfrak{B}\) of l∞ (Xi) such that \(\mathfrak{B}\) is α-off the origin.
中文翻译:
对偶空间和Banach序列空间的球覆盖特性
在本文中,我们证明(X,p)是可分离的,当且仅当存在w *-下半连续范数序列\(\ left \ {{{p_n}} \ right \} _ {n = 1} ^(X *,p)的\ infty \),使得(1)存在一个X *的密集子集G n,使得p n是在G n和dp n(G n)X上对于所有n ∊ N可微的Gâteaux微分。; (2)p Ñ ≤ p和p Ñ → p统一在X *的每个有界子集上;(3)为任何α∈(0,1),存在球覆盖\(\左\ {{B \左({X_ {I,N} ^ *,{R_ {I,N}}} \右)} \右\} _ {i = 1} ^ \ infty \)的(X *,p ñ),使得它是α -off原点和X * I,N ∈ ģ ñ。此外,我们还证明了如果X我是糕点可微空间,则存在的实数α > 0和球覆盖\(\ mathfrak {B} _i \)的X我使得\(\ mathfrak {B } _i \)是 α -off原点,当且仅当存在实数α > 0和球覆盖\(\ mathfrak {B} \)的升∞(X我),使得\(\ mathfrak {B} \)是α-偏离原点。