<p>Given a metrizable space <i>Z</i>,&#xa0; denote by <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43036_2025_471_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="52" /> </InlineMediaObject> <EquationSource Format="TEX">\(\operatorname {PM}(Z)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>PM</mo> <mo stretchy="false">(</mo> <mi>Z</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> the space of continuous bounded pseudometrics on <i>Z</i>,&#xa0; and denote by <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43036_2025_471_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="53" /> </InlineMediaObject> <EquationSource Format="TEX">\(\operatorname {AM}(Z)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>AM</mo> <mo stretchy="false">(</mo> <mi>Z</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> the one of continuous bounded admissible metrics on <i>Z</i>,&#xa0; both of which are equipped with the sup-norm <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43036_2025_471_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="37" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Vert \cdot \Vert .\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">‖</mo> <mo>·</mo> <mo stretchy="false">‖</mo> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation> In this paper, we shall prove Banach–Stone type theorems on spaces of metrics, that is, for metrizable spaces <i>X</i> and <i>Y</i>,&#xa0; <i>X</i> and <i>Y</i> are homeomorphic if and only if there exists a surjective isometry <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43036_2025_471_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="159" /> </InlineMediaObject> <EquationSource Format="TEX">\(T: \operatorname {PM}(X) \rightarrow \operatorname {PM}(Y)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>T</mi> <mo>:</mo> <mo>PM</mo> <mo stretchy="false">(</mo> <mi>X</mi> <mo stretchy="false">)</mo> <mo stretchy="false">→</mo> <mo>PM</mo> <mo stretchy="false">(</mo> <mi>Y</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43036_2025_471_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="173" /> </InlineMediaObject> <EquationSource Format="TEX">\((T: \operatorname {AM}(X) \rightarrow \operatorname {AM}(Y))\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>T</mi> <mo>:</mo> <mo>AM</mo> <mo stretchy="false">(</mo> <mi>X</mi> <mo stretchy="false">)</mo> <mo stretchy="false">→</mo> <mo>AM</mo> <mo stretchy="false">(</mo> <mi>Y</mi> <mo stretchy="false">)</mo> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> satisfying some conditions. Then for each surjective isometry <i>T</i>,&#xa0; there is a homeomorphism <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43036_2025_471_Article_IEq6.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="84" /> </InlineMediaObject> <EquationSource Format="TEX">\(\phi : Y \rightarrow X\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>ϕ</mi> <mo>:</mo> <mi>Y</mi> <mo stretchy="false">→</mo> <mi>X</mi> </mrow> </math></EquationSource> </InlineEquation> such that for any <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43036_2025_471_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="85" /> </InlineMediaObject> <EquationSource Format="TEX">\(d \in \operatorname {PM}(X)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>d</mi> <mo>∈</mo> <mo>PM</mo> <mo stretchy="false">(</mo> <mi>X</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> and for any <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43036_2025_471_Article_IEq8.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="65" /> </InlineMediaObject> <EquationSource Format="TEX">\(x, y \in Y,\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>x</mi> <mo>,</mo> <mi>y</mi> <mo>∈</mo> <mi>Y</mi> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43036_2025_471_Article_IEq9.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="191" /> </InlineMediaObject> <EquationSource Format="TEX">\(T(d)(x,y) = d(\phi (x),\phi (y)).\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>T</mi> <mo stretchy="false">(</mo> <mi>d</mi> <mo stretchy="false">)</mo> <mo stretchy="false">(</mo> <mi>x</mi> <mo>,</mo> <mi>y</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mi>d</mi> <mo stretchy="false">(</mo> <mi>ϕ</mi> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> <mo>,</mo> <mi>ϕ</mi> <mo stretchy="false">(</mo> <mi>y</mi> <mo stretchy="false">)</mo> <mo stretchy="false">)</mo> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation> Except for the case where the cardinality of <i>X</i> or <i>Y</i> is equal to 2,&#xa0; the homeomorphism <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43036_2025_471_Article_IEq10.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="16" /> </InlineMediaObject> <EquationSource Format="TEX">\(\phi \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ϕ</mi> </math></EquationSource> </InlineEquation> can be chosen uniquely.</p>

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Isometries between spaces of metrics

  • Katsuhisa Koshino

摘要

Given a metrizable space Z,  denote by \(\operatorname {PM}(Z)\) PM ( Z ) the space of continuous bounded pseudometrics on Z,  and denote by \(\operatorname {AM}(Z)\) AM ( Z ) the one of continuous bounded admissible metrics on Z,  both of which are equipped with the sup-norm \(\Vert \cdot \Vert .\) · . In this paper, we shall prove Banach–Stone type theorems on spaces of metrics, that is, for metrizable spaces X and YX and Y are homeomorphic if and only if there exists a surjective isometry \(T: \operatorname {PM}(X) \rightarrow \operatorname {PM}(Y)\) T : PM ( X ) PM ( Y ) \((T: \operatorname {AM}(X) \rightarrow \operatorname {AM}(Y))\) ( T : AM ( X ) AM ( Y ) ) satisfying some conditions. Then for each surjective isometry T,  there is a homeomorphism \(\phi : Y \rightarrow X\) ϕ : Y X such that for any \(d \in \operatorname {PM}(X)\) d PM ( X ) and for any \(x, y \in Y,\) x , y Y , \(T(d)(x,y) = d(\phi (x),\phi (y)).\) T ( d ) ( x , y ) = d ( ϕ ( x ) , ϕ ( y ) ) . Except for the case where the cardinality of X or Y is equal to 2,  the homeomorphism \(\phi \) ϕ can be chosen uniquely.