English

Some new results on functions in $C(X)$ having their support on ideals of closed sets

General Topology 2017-12-29 v1

Abstract

For any ideal P\mathcal{P} of closed sets in XX, let CP(X)C_\mathcal{P}(X) be the family of those functions in C(X)C(X) whose support lie on P\mathcal{P}. Further let CP(X)C^\mathcal{P}_\infty(X) contain precisely those functions ff in C(X)C(X) for which for each ϵ>0,{xX:f(x)ϵ}\epsilon >0, \{x\in X: \lvert f(x)\rvert\geq \epsilon\} is a member of P\mathcal{P}. Let υCPX\upsilon_{C_{\mathcal{P}}}X stand for the set of all those points pp in βX\beta X at which the stone extension ff^* for each ff in CP(X)C_\mathcal{P}(X) is real valued. We show that each realcompact space lying between XX and βX\beta X is of the form υCPX\upsilon_{C_\mathcal{P}}X if and only if XX is pseudocompact. We find out conditions under which an arbitrary product of spaces of the form locally-P/\mathcal{P}/ almost locally-P\mathcal{P}, becomes a space of the same form. We further show that CP(X)C_\mathcal{P}(X) is a free ideal ( essential ideal ) of C(X)C(X) if and only if CP(X)C^\mathcal{P}_\infty(X) is a free ideal ( respectively essential ideal ) of C(X)+CP(X)C^*(X)+C^\mathcal{P}_\infty(X) when and only when XX is locally-P\mathcal{P} ( almost locally-P\mathcal{P}). We address the problem, when does CP(X)/CP(X)C_\mathcal{P}(X)/C^\mathcal{P}_{\infty}(X) become identical to the socle of the ring C(X)C(X). Finally we observe that the ideals of the form CP(X)C_\mathcal{P}(X) of C(X)C(X) are no other than the zz^\circ-ideals of C(X)C(X).

Keywords

Cite

@article{arxiv.1712.09820,
  title  = {Some new results on functions in $C(X)$ having their support on ideals of closed sets},
  author = {Sagarmoy Bag and Sudip Kumar Acharyya and Pritam Rooj and Goutam Bhunia},
  journal= {arXiv preprint arXiv:1712.09820},
  year   = {2017}
}