<p>This paper investigates the interplay between properties of a topological space <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(X\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>X</mi> </math></EquationSource> </InlineEquation>, in particular of its natural order, and properties of the lax comma category <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\textsf{Top}{\,\Downarrow \,}X\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="sans-serif">Top</mi> <mrow> <mspace width="0.166667em" /> <mo stretchy="false">⇓</mo> <mspace width="0.166667em" /> </mrow> <mi>X</mi> </mrow> </math></EquationSource> </InlineEquation>, where <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\textsf{Top}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="sans-serif">Top</mi> </math></EquationSource> </InlineEquation> denotes the category of topological spaces and continuous maps. Namely, it is shown that, whenever <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(X\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>X</mi> </math></EquationSource> </InlineEquation> is a topological <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\bigwedge \)</EquationSource> <EquationSource Format="MATHML"><math> <mo>⋀</mo> </math></EquationSource> </InlineEquation>-semilattice, the canonical forgetful functor <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\textsf{Top}{\,\Downarrow \,}X\rightarrow \textsf{Top}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="sans-serif">Top</mi> <mrow> <mspace width="0.166667em" /> <mo stretchy="false">⇓</mo> <mspace width="0.166667em" /> </mrow> <mi>X</mi> <mo stretchy="false">→</mo> <mi mathvariant="sans-serif">Top</mi> </mrow> </math></EquationSource> </InlineEquation> is topological, preserves and reflects exponentials, and preserves effective descent morphisms. Moreover, under additional conditions on <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(X\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>X</mi> </math></EquationSource> </InlineEquation>, a characterisation of effective descent morphisms is obtained.</p>

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Topological Lax Comma Categories

  • Maria Manuel Clementino,
  • Dirk Hofmann,
  • Rui Prezado

摘要

This paper investigates the interplay between properties of a topological space \(X\) X , in particular of its natural order, and properties of the lax comma category \(\textsf{Top}{\,\Downarrow \,}X\) Top X , where \(\textsf{Top}\) Top denotes the category of topological spaces and continuous maps. Namely, it is shown that, whenever \(X\) X is a topological \(\bigwedge \) -semilattice, the canonical forgetful functor \(\textsf{Top}{\,\Downarrow \,}X\rightarrow \textsf{Top}\) Top X Top is topological, preserves and reflects exponentials, and preserves effective descent morphisms. Moreover, under additional conditions on \(X\) X , a characterisation of effective descent morphisms is obtained.