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On metrizable subspaces and quotients of non-Archimedean spaces $$C_p(X, {\mathbb {K}})$$Cp(X,K)
Revista de la Real Academia de Ciencias Exactas, Físicas y Naturales. Serie A. Matemáticas ( IF 1.8 ) Pub Date : 2020-05-07 , DOI: 10.1007/s13398-020-00849-9
Jerzy Ka̧kol , Wiesław Śliwa

Let \({\mathbb {K}}\) be a non-trivially valued non-Archimedean complete field. Let \(\ell _{\infty }({\mathbb {N}}, {\mathbb {K}})\) [\(\ell _c({\mathbb {N}}, {\mathbb {K}});\)\(c_0({\mathbb {N}}, {\mathbb {K}})\)] be the space of all sequences in \({\mathbb {K}}\) that are bounded [relatively compact; convergent to 0] with the topology of pointwise convergence (i.e. with the topology induced from \({\mathbb {K}}^{{\mathbb {N}}}\)). Let X be an infinite ultraregular space and let \(C_p(X,{\mathbb {K}})\) be the space of all continuous functions from X to \({\mathbb {K}}\) endowed with the topology of pointwise convergence. It is easy to see that \(C_p(X,{\mathbb {K}})\) is metrizable if and only if X is countable. We show that for any X [with an infinite compact subset] the space \(C_p(X,{\mathbb {K}})\) has an infinite-dimensional [closed] metrizable subspace isomorphic to \(c_0({\mathbb {N}}, {\mathbb {K}})\). Next we prove that \(C_p(X,{\mathbb {K}})\) has a quotient isomorphic to \(c_0({\mathbb {N}}, {\mathbb {K}})\) if and only if it has a complemented subspace isomorphic to \(c_0({\mathbb {N}}, {\mathbb {K}})\). It follows that for any extremally disconnected compact space X the space \(C_p(X,{\mathbb {K}})\) has no quotient isomorphic to the space \(c_0({\mathbb {N}}, {\mathbb {K}})\); in particular, for any infinite discrete space D the space \(C_p(\beta D, {\mathbb {K}})\) has no quotient isomorphic \(c_0({\mathbb {N}}, {\mathbb {K}})\). Finally we investigate the question for which X the space \(C_p(X,{\mathbb {K}})\) has an infinite-dimensional metrizable quotient. We show that for any infinite discrete space D the space \(C_p(\beta D, {\mathbb {K}})\) has an infinite-dimensional metrizable quotient isomorphic to some subspace \(\ell _c^0({\mathbb {N}}, {\mathbb {K}})\) of \({\mathbb {K}}^{{\mathbb {N}}}\). If \({\mathbb {K}}\) is locally compact then \(\ell _c^0({\mathbb {N}}, {\mathbb {K}})=\ell _{\infty }({\mathbb {N}}, {\mathbb {K}})\). If \(|n1_{{\mathbb {K}}}|\ne 1\) for some \(n\in {\mathbb {N}}\), then \(\ell _c^0({\mathbb {N}}, {\mathbb {K}})=\ell _c ({\mathbb {N}}, {\mathbb {K}}).\) In particular, \(C_p(\beta D, {\mathbb {Q}}_q)\) has a quotient isomorphic to \(\ell _{\infty }({\mathbb {N}}, {\mathbb {Q}}_q)\) and \(C_p(\beta D, {\mathbb {C}}_q)\) has a quotient isomorphic to \(\ell _c({\mathbb {N}}, {\mathbb {C}}_q)\) for any prime number q.



中文翻译:

关于非阿西米德空间的可商化子空间和商$$ C_p(X,{\ mathbb {K}})$$ Cp(X,K)

\({\ mathbb {K}} \)为一个非平凡的非阿基米德完整字段。令\(\ ell _ {\ infty}({\ mathbb {N}},{\ mathbb {K}})\) [ [ \(\ ell _c({\ mathbb {N}},{\ mathbb {K} }); \)\(c_0({\ mathbb {N}},{\ mathbb {K}})\) ]是\({\ mathbb {K}} \\}中所有有界[相对紧凑;使用逐点收敛的拓扑(即\({\ mathbb {K}} ^ {{\ mathbb {N}}} \)诱导的拓扑收敛到0] )。令X为无限的超规则空间,令\(C_p(X,{\ mathbb {K}})\)为从X\({\ mathbb {K}} \)的所有连续函数的空间具有逐点收敛的拓扑。很容易看到\(C_p(X,{\ mathbb {K}})\)是可量化的,且仅当X是可数的。我们表明,对于任何X [具有无限紧凑子集],空间\(C_p(X,{\ mathbb {K}})\)具有与\(c_0({{mathbb {N}},{\ mathbb {K}})\)。接下来,我们证明了\(C_P(X,{\ mathbb {K}})\)具有商同构于\(C_0({\ mathbb {N}},{\ mathbb {K}})\),当且仅如果它具有\(c_0({\ mathbb {N}},{\ mathbb {K}})\)同构的互补子空间。因此,对于任何极端断开的紧凑空间X空间\(C_p(X,{\ mathbb {K}})\)与空间\(c_0({\ mathbb {N}},{\ mathbb {K}})\)没有同构。特别是,对于任何无限离散空间D,空间\(C_p(\ beta D,{\ mathbb {K}})\)没有商同构\(c_0({\ mathbb {N}},{\ mathbb {K }})\)。最后,我们探讨这问题X的空间\(C_P(X,{\ mathbb {K}})\)具有无限维度量化商。我们证明,对于任何无限离散空间D,空间\(C_p(\ beta D,{\ mathbb {K}})\)具有对某些子空间同构的无限维可商化商\(\ ELL _c ^ 0({\ mathbb {N}},{\ mathbb {K}})\)\({\ mathbb {K}} ^ {{\ mathbb {N}}} \)。如果\({\ mathbb {K}} \)是局部紧凑的,则\(\ ell _c ^ 0({\ mathbb {N}},{\ mathbb {K}})= \ ell _ {\ infty}({ \ mathbb {N}},{\ mathbb {K}})\)。如果\(| n1 _ {{\ mathbb {K}}} | \ ne 1 \)对于某些\(n \ in {\ mathbb {N}} \),则\(\ ell _c ^ 0({\ mathbb { N}},{\ mathbb {K}})= \ ell _c({\ mathbb {N}},{\ mathbb {K}})。\)特别是\(C_p(\ beta D,{\ mathbb {Q}} _ q)\)\(\ ell _ {\ infty}({\ mathbb {N}},{\ mathbb {Q}} _ q)\)\(C_p(\ beta D ,{\ mathbb {C}} _​​ q)\)的商同构\(\ ell _c({\ mathbb {N}},{\ mathbb {C}} _​​ q)\)对于任何质数q

更新日期:2020-05-07
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