<p>A submodule <i>N</i> of an <i>R</i>-module <i>M</i> is lifting if <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\text {Ann}_R(\frac{M}{N})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mtext>Ann</mtext> <mi>R</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mfrac> <mi>M</mi> <mi>N</mi> </mfrac> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> is a lifting ideal of <i>R</i>, i.e., if <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(r(1-r)M\subseteq N\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>r</mi> <mo stretchy="false">(</mo> <mn>1</mn> <mo>-</mo> <mi>r</mi> <mo stretchy="false">)</mo> <mi>M</mi> <mo>⊆</mo> <mi>N</mi> </mrow> </math></EquationSource> </InlineEquation> for some <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(r\in R\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>r</mi> <mo>∈</mo> <mi>R</mi> </mrow> </math></EquationSource> </InlineEquation>, then there exists an idempotent <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(e\in R\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>e</mi> <mo>∈</mo> <mi>R</mi> </mrow> </math></EquationSource> </InlineEquation> such that <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\((r-e)M\subseteq N\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>r</mi> <mo>-</mo> <mi>e</mi> <mo stretchy="false">)</mo> <mi>M</mi> <mo>⊆</mo> <mi>N</mi> </mrow> </math></EquationSource> </InlineEquation>. We show that <i>R</i> is a clean ring if and only if every submodule of any <i>R</i>-module <i>M</i> is lifting. A lifting comaximal decomposition of a submodule <i>N</i> of an <i>R</i>-module <i>M</i> is <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(N=\displaystyle \bigcap _{i=1}^{n}N_i\)</EquationSource> <EquationSource Format="MATHML"><math> <mstyle displaystyle="true" scriptlevel="0"> <mrow> <mi>N</mi> <mo>=</mo> <munderover> <mo>⋂</mo> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>n</mi> </munderover> <msub> <mi>N</mi> <mi>i</mi> </msub> </mrow> </mstyle> </math></EquationSource> </InlineEquation>, where <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(N_i's\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>N</mi> <mi>i</mi> <mo>′</mo> </msubsup> <mi>s</mi> </mrow> </math></EquationSource> </InlineEquation> are lifting submodules of <i>M</i> such that <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\((N_i:M)+(N_j:M)=R\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo stretchy="false">(</mo> <msub> <mi>N</mi> <mi>i</mi> </msub> <mo>:</mo> <mi>M</mi> <mo stretchy="false">)</mo> </mrow> <mo>+</mo> <mrow> <mo stretchy="false">(</mo> <msub> <mi>N</mi> <mi>j</mi> </msub> <mo>:</mo> <mi>M</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mi>R</mi> </mrow> </math></EquationSource> </InlineEquation>, for all <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(i\ne j\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>i</mi> <mo>≠</mo> <mi>j</mi> </mrow> </math></EquationSource> </InlineEquation>. If <i>R</i> is a Noetherian ring and <i>M</i> is a finitely generated multiplication <i>R</i>-module, then we show that every proper submodule of <i>M</i> has a unique (up to order) lifting comaximal decomposition. We will also examine lifting submodules from the point of view of the Zariski topology.</p>

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Lifting comaximal decomposition

  • R. Nekooei

摘要

A submodule N of an R-module M is lifting if \(\text {Ann}_R(\frac{M}{N})\) Ann R ( M N ) is a lifting ideal of R, i.e., if \(r(1-r)M\subseteq N\) r ( 1 - r ) M N for some \(r\in R\) r R , then there exists an idempotent \(e\in R\) e R such that \((r-e)M\subseteq N\) ( r - e ) M N . We show that R is a clean ring if and only if every submodule of any R-module M is lifting. A lifting comaximal decomposition of a submodule N of an R-module M is \(N=\displaystyle \bigcap _{i=1}^{n}N_i\) N = i = 1 n N i , where \(N_i's\) N i s are lifting submodules of M such that \((N_i:M)+(N_j:M)=R\) ( N i : M ) + ( N j : M ) = R , for all \(i\ne j\) i j . If R is a Noetherian ring and M is a finitely generated multiplication R-module, then we show that every proper submodule of M has a unique (up to order) lifting comaximal decomposition. We will also examine lifting submodules from the point of view of the Zariski topology.