<p>Given an ideal <i>I</i> in the ring <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="70" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {M}(X,\mathcal {A})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">M</mi> <mo stretchy="false">(</mo> <mi>X</mi> <mo>,</mo> <mi mathvariant="script">A</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> of all real valued measurable functions over the measurable space <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="50" /> </InlineMediaObject> <EquationSource Format="TEX">\((X,\mathcal {A})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo>,</mo> <mi mathvariant="script">A</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> and a measure <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="109" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mu :\mathcal {A}\rightarrow [0,\infty ]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mo>:</mo> <mi mathvariant="script">A</mi> <mo stretchy="false">→</mo> <mo stretchy="false">[</mo> <mn>0</mn> <mo>,</mo> <mi>∞</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation>, we introduce the <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq4.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="20" /> </InlineMediaObject> <EquationSource Format="TEX">\(u_\mu ^I\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>u</mi> <mi>μ</mi> <mi>I</mi> </msubsup> </math></EquationSource> </InlineEquation>-topology and the <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq5.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="25" /> </InlineMediaObject> <EquationSource Format="TEX">\(m_\mu ^I\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>m</mi> <mi>μ</mi> <mi>I</mi> </msubsup> </math></EquationSource> </InlineEquation>-topology on <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="70" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {M}(X,\mathcal {A})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">M</mi> <mo stretchy="false">(</mo> <mi>X</mi> <mo>,</mo> <mi mathvariant="script">A</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> as generalizations of the <i>u</i>-topology and the <i>m</i>-topology on <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="70" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {M}(X,\mathcal {A})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">M</mi> <mo stretchy="false">(</mo> <mi>X</mi> <mo>,</mo> <mi mathvariant="script">A</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> respectively. For a countably generated ideal <i>I</i> in <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="70" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {M}(X,\mathcal {A})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">M</mi> <mo stretchy="false">(</mo> <mi>X</mi> <mo>,</mo> <mi mathvariant="script">A</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, it is proved that the <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq4.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="20" /> </InlineMediaObject> <EquationSource Format="TEX">\(u_\mu ^I\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>u</mi> <mi>μ</mi> <mi>I</mi> </msubsup> </math></EquationSource> </InlineEquation>-topology and the <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq5.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="25" /> </InlineMediaObject> <EquationSource Format="TEX">\(m_\mu ^I\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>m</mi> <mi>μ</mi> <mi>I</mi> </msubsup> </math></EquationSource> </InlineEquation>-topology coincide if and only if <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq11.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="81" /> </InlineMediaObject> <EquationSource Format="TEX">\(X\setminus \bigcap Z[I]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>X</mi> <mo lspace="0.15em" rspace="0.15em" stretchy="false">\</mo> <mo>⋂</mo> <mi>Z</mi> <mo stretchy="false">[</mo> <mi>I</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> is a <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq12.gif" Format="GIF" Height="12" Rendition="HTML" Resolution="72" Type="Linedraw" Width="15" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mu \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>μ</mi> </math></EquationSource> </InlineEquation>-bounded subset of <i>X</i>. The components of 0 in both of these topologies are determined and it is proved that the condition of denseness of an ideal <i>I</i> in <InlineEquation ID="IEq13"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="70" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {M}(X,\mathcal {A})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">M</mi> <mo stretchy="false">(</mo> <mi>X</mi> <mo>,</mo> <mi mathvariant="script">A</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is equivalent in these two topologies and this happens when and only when there exists <InlineEquation ID="IEq14"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq14.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="66" /> </InlineMediaObject> <EquationSource Format="TEX">\(Z\in Z[I]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>Z</mi> <mo>∈</mo> <mi>Z</mi> <mo stretchy="false">[</mo> <mi>I</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> such that <InlineEquation ID="IEq15"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq15.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="68" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mu (Z)=0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mo stretchy="false">(</mo> <mi>Z</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>. It is also proved that <i>I</i> is closed in <InlineEquation ID="IEq16"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="70" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {M}(X,\mathcal {A})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">M</mi> <mo stretchy="false">(</mo> <mi>X</mi> <mo>,</mo> <mi mathvariant="script">A</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> in the <InlineEquation ID="IEq17"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq17.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="25" /> </InlineMediaObject> <EquationSource Format="TEX">\(m_\mu \)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>m</mi> <mi>μ</mi> </msub> </math></EquationSource> </InlineEquation>-topology if and only if it is a <InlineEquation ID="IEq18"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq18.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="22" /> </InlineMediaObject> <EquationSource Format="TEX">\(Z_\mu \)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>Z</mi> <mi>μ</mi> </msub> </math></EquationSource> </InlineEquation>-ideal. Two more topologies on <InlineEquation ID="IEq19"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="70" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {M}(X,\mathcal {A})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">M</mi> <mo stretchy="false">(</mo> <mi>X</mi> <mo>,</mo> <mi mathvariant="script">A</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> viz. the <InlineEquation ID="IEq20"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq20.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="31" /> </InlineMediaObject> <EquationSource Format="TEX">\(u_{\mu ,F}^I\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>u</mi> <mrow> <mi>μ</mi> <mo>,</mo> <mi>F</mi> </mrow> <mi>I</mi> </msubsup> </math></EquationSource> </InlineEquation>-topology and the <InlineEquation ID="IEq21"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq21.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="36" /> </InlineMediaObject> <EquationSource Format="TEX">\(m_{\mu ,F}^I\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>m</mi> <mrow> <mi>μ</mi> <mo>,</mo> <mi>F</mi> </mrow> <mi>I</mi> </msubsup> </math></EquationSource> </InlineEquation>-topology, finer than the <InlineEquation ID="IEq22"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq4.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="20" /> </InlineMediaObject> <EquationSource Format="TEX">\(u_\mu ^I\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>u</mi> <mi>μ</mi> <mi>I</mi> </msubsup> </math></EquationSource> </InlineEquation>-topology and the <InlineEquation ID="IEq23"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12_2025_896_Article_IEq5.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="25" /> </InlineMediaObject> <EquationSource Format="TEX">\(m_\mu ^I\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>m</mi> <mi>μ</mi> <mi>I</mi> </msubsup> </math></EquationSource> </InlineEquation>-topology respectively are introduced and a few relevant properties are investigated thereon.</p>

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u-topology and m-topology on the ring of measurable functions, generalized and revisited

  • Sudip Kumar Acharyya,
  • Atasi Debray,
  • Pratip Nandi

摘要

Given an ideal I in the ring \(\mathcal {M}(X,\mathcal {A})\) M ( X , A ) of all real valued measurable functions over the measurable space \((X,\mathcal {A})\) ( X , A ) and a measure \(\mu :\mathcal {A}\rightarrow [0,\infty ]\) μ : A [ 0 , ] , we introduce the \(u_\mu ^I\) u μ I -topology and the \(m_\mu ^I\) m μ I -topology on \(\mathcal {M}(X,\mathcal {A})\) M ( X , A ) as generalizations of the u-topology and the m-topology on \(\mathcal {M}(X,\mathcal {A})\) M ( X , A ) respectively. For a countably generated ideal I in \(\mathcal {M}(X,\mathcal {A})\) M ( X , A ) , it is proved that the \(u_\mu ^I\) u μ I -topology and the \(m_\mu ^I\) m μ I -topology coincide if and only if \(X\setminus \bigcap Z[I]\) X \ Z [ I ] is a \(\mu \) μ -bounded subset of X. The components of 0 in both of these topologies are determined and it is proved that the condition of denseness of an ideal I in \(\mathcal {M}(X,\mathcal {A})\) M ( X , A ) is equivalent in these two topologies and this happens when and only when there exists \(Z\in Z[I]\) Z Z [ I ] such that \(\mu (Z)=0\) μ ( Z ) = 0 . It is also proved that I is closed in \(\mathcal {M}(X,\mathcal {A})\) M ( X , A ) in the \(m_\mu \) m μ -topology if and only if it is a \(Z_\mu \) Z μ -ideal. Two more topologies on \(\mathcal {M}(X,\mathcal {A})\) M ( X , A ) viz. the \(u_{\mu ,F}^I\) u μ , F I -topology and the \(m_{\mu ,F}^I\) m μ , F I -topology, finer than the \(u_\mu ^I\) u μ I -topology and the \(m_\mu ^I\) m μ I -topology respectively are introduced and a few relevant properties are investigated thereon.