<p>For a topological space <i>X</i>, let <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\mathcal {S}}[X]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">S</mi> <mo stretchy="false">[</mo> <mi>X</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> denote the hyperspace of finite unions of convergent sequences endowed with the Pixley–Roy topology. In this paper, we give a characterization of convergent sequences in <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({\mathcal {S}}[X]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">S</mi> <mo stretchy="false">[</mo> <mi>X</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation>. Then we consider some cardinal invariants on <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\({\mathcal {S}}[X]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">S</mi> <mo stretchy="false">[</mo> <mi>X</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation>, and compare the character, the pseudocharacter, the <i>sn</i>-character, the <i>cs</i>-character, the <i>cn</i>-character and the <i>ck</i>-character of <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\({\mathcal {S}}[X]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">S</mi> <mo stretchy="false">[</mo> <mi>X</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> with the corresponding cardinal function of <i>X</i>. Moreover, the metrizability and the countable fan tightness of <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\({\mathcal {S}}[X]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">S</mi> <mo stretchy="false">[</mo> <mi>X</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> are discussed. Further, some characterizations of the chain conditions and the weak Lindelöf degree of <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\({\mathcal {S}}[X]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">S</mi> <mo stretchy="false">[</mo> <mi>X</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> are provided.</p>

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Pixley–Roy hyperspace of finite unions of convergent sequences

  • Jingling Lin,
  • Xiaoquan Xu

摘要

For a topological space X, let \({\mathcal {S}}[X]\) S [ X ] denote the hyperspace of finite unions of convergent sequences endowed with the Pixley–Roy topology. In this paper, we give a characterization of convergent sequences in \({\mathcal {S}}[X]\) S [ X ] . Then we consider some cardinal invariants on \({\mathcal {S}}[X]\) S [ X ] , and compare the character, the pseudocharacter, the sn-character, the cs-character, the cn-character and the ck-character of \({\mathcal {S}}[X]\) S [ X ] with the corresponding cardinal function of X. Moreover, the metrizability and the countable fan tightness of \({\mathcal {S}}[X]\) S [ X ] are discussed. Further, some characterizations of the chain conditions and the weak Lindelöf degree of \({\mathcal {S}}[X]\) S [ X ] are provided.