<p>Let <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2133_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="44" /> </InlineMediaObject> <EquationSource Format="TEX">\((Q, \mathfrak {n} )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>Q</mi> <mo>,</mo> <mi mathvariant="fraktur">n</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> be a regular local ring and let <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2133_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="105" /> </InlineMediaObject> <EquationSource Format="TEX">\(f_1, \ldots , f_c \in \mathfrak {n} ^2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>f</mi> <mi>c</mi> </msub> <mo>∈</mo> <msup> <mrow> <mi mathvariant="fraktur">n</mi> </mrow> <mn>2</mn> </msup> </mrow> </math></EquationSource> </InlineEquation> be a <i>Q</i>-regular sequence. Set <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2133_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="164" /> </InlineMediaObject> <EquationSource Format="TEX">\((A, \mathfrak {m} ) = (Q/(\textbf{f} ), \mathfrak {n} /(\textbf{f} ))\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>A</mi> <mo>,</mo> <mi mathvariant="fraktur">m</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mo stretchy="false">(</mo> <mi>Q</mi> <mo stretchy="false">/</mo> <mo stretchy="false">(</mo> <mi mathvariant="bold">f</mi> <mo stretchy="false">)</mo> <mo>,</mo> <mi mathvariant="fraktur">n</mi> <mo stretchy="false">/</mo> <mo stretchy="false">(</mo> <mi mathvariant="bold">f</mi> <mo stretchy="false">)</mo> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>. Further assume that the initial forms <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2133_Article_IEq4.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="75" /> </InlineMediaObject> <EquationSource Format="TEX">\(f_1^*, \ldots , f_c^*\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>f</mi> <mn>1</mn> <mo>∗</mo> </msubsup> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msubsup> <mi>f</mi> <mi>c</mi> <mo>∗</mo> </msubsup> </mrow> </math></EquationSource> </InlineEquation> form a <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2133_Article_IEq5.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="157" /> </InlineMediaObject> <EquationSource Format="TEX">\(G(Q) = \bigoplus _{n \ge 0}\mathfrak {n} ^i/\mathfrak {n} ^{i+1}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>G</mi> <mrow> <mo stretchy="false">(</mo> <mi>Q</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msub> <mo>⨁</mo> <mrow> <mi>n</mi> <mo>≥</mo> <mn>0</mn> </mrow> </msub> <msup> <mrow> <mi mathvariant="fraktur">n</mi> </mrow> <mi>i</mi> </msup> <mo stretchy="false">/</mo> <msup> <mrow> <mi mathvariant="fraktur">n</mi> </mrow> <mrow> <mi>i</mi> <mo>+</mo> <mn>1</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation>-regular sequence. Without loss of any generality, assume <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2133_Article_IEq6.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="268" /> </InlineMediaObject> <EquationSource Format="TEX">\(\operatorname {ord}_Q(f_1) \ge \operatorname {ord}_Q(f_2) \ge \cdots \ge \operatorname {ord}_Q(f_c)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mo>ord</mo> <mi>Q</mi> </msub> <mrow> <mo stretchy="false">(</mo> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo stretchy="false">)</mo> </mrow> <mo>≥</mo> <msub> <mo>ord</mo> <mi>Q</mi> </msub> <mrow> <mo stretchy="false">(</mo> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo stretchy="false">)</mo> </mrow> <mo>≥</mo> <mo>⋯</mo> <mo>≥</mo> <msub> <mo>ord</mo> <mi>Q</mi> </msub> <mrow> <mo stretchy="false">(</mo> <msub> <mi>f</mi> <mi>c</mi> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. Let <i>M</i> be a finitely generated <i>A</i>-module and let <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2133_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="41" /> </InlineMediaObject> <EquationSource Format="TEX">\((\mathbb {F} , \partial )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="double-struck">F</mi> <mo>,</mo> <mi>∂</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> be a minimal free resolution of <i>M</i>. Then we prove that <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2133_Article_IEq8.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="161" /> </InlineMediaObject> <EquationSource Format="TEX">\(\operatorname {ord}(\partial _i) \le \operatorname {ord}_Q(f_1) - 1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>ord</mo> <mrow> <mo stretchy="false">(</mo> <msub> <mi>∂</mi> <mi>i</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mo>≤</mo> <msub> <mo>ord</mo> <mi>Q</mi> </msub> <mrow> <mo stretchy="false">(</mo> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation> for all <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2133_Article_IEq9.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">\(i \gg 0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>i</mi> <mo>≫</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>. We also construct an MCM <i>A</i>-module <i>M</i> such that <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2133_Article_IEq10.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="181" /> </InlineMediaObject> <EquationSource Format="TEX">\(\operatorname {ord}(\partial _{2i+1}) = \operatorname {ord}_Q(f_1) - 1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>ord</mo> <mrow> <mo stretchy="false">(</mo> <msub> <mi>∂</mi> <mrow> <mn>2</mn> <mi>i</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msub> <mo>ord</mo> <mi>Q</mi> </msub> <mrow> <mo stretchy="false">(</mo> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation> for all <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2133_Article_IEq11.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="38" /> </InlineMediaObject> <EquationSource Format="TEX">\(i \ge 0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>i</mi> <mo>≥</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>. We also give a considerably simpler proof regarding the periodicity of ideals of minors of maps in a minimal free resolution of modules over arbitrary complete intersection rings (not necessarily strict).</p>

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Resolutions over strict complete intersections

  • Tony J. Puthenpurakal

摘要

Let \((Q, \mathfrak {n} )\) ( Q , n ) be a regular local ring and let \(f_1, \ldots , f_c \in \mathfrak {n} ^2\) f 1 , , f c n 2 be a Q-regular sequence. Set \((A, \mathfrak {m} ) = (Q/(\textbf{f} ), \mathfrak {n} /(\textbf{f} ))\) ( A , m ) = ( Q / ( f ) , n / ( f ) ) . Further assume that the initial forms \(f_1^*, \ldots , f_c^*\) f 1 , , f c form a \(G(Q) = \bigoplus _{n \ge 0}\mathfrak {n} ^i/\mathfrak {n} ^{i+1}\) G ( Q ) = n 0 n i / n i + 1 -regular sequence. Without loss of any generality, assume \(\operatorname {ord}_Q(f_1) \ge \operatorname {ord}_Q(f_2) \ge \cdots \ge \operatorname {ord}_Q(f_c)\) ord Q ( f 1 ) ord Q ( f 2 ) ord Q ( f c ) . Let M be a finitely generated A-module and let \((\mathbb {F} , \partial )\) ( F , ) be a minimal free resolution of M. Then we prove that \(\operatorname {ord}(\partial _i) \le \operatorname {ord}_Q(f_1) - 1\) ord ( i ) ord Q ( f 1 ) - 1 for all \(i \gg 0\) i 0 . We also construct an MCM A-module M such that \(\operatorname {ord}(\partial _{2i+1}) = \operatorname {ord}_Q(f_1) - 1\) ord ( 2 i + 1 ) = ord Q ( f 1 ) - 1 for all \(i \ge 0\) i 0 . We also give a considerably simpler proof regarding the periodicity of ideals of minors of maps in a minimal free resolution of modules over arbitrary complete intersection rings (not necessarily strict).