<p>Let <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11587_2025_947_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="34" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mu (I)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mo stretchy="false">(</mo> <mi>I</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> denote the number of generators of the ideal <i>I</i>. It is well known that <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11587_2025_947_Article_IEq2.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="41" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mu (I^{k})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mo stretchy="false">(</mo> <msup> <mi>I</mi> <mi>k</mi> </msup> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a polynomial for <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11587_2025_947_Article_IEq3.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="46" /> </InlineMediaObject> <EquationSource Format="TEX">\(k\gg 0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>≫</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>; thus, <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11587_2025_947_Article_IEq4.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="117" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mu (I^{k})&lt;\mu (I^{k+1})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mrow> <mo stretchy="false">(</mo> <msup> <mi>I</mi> <mi>k</mi> </msup> <mo stretchy="false">)</mo> </mrow> <mo>&lt;</mo> <mi>μ</mi> <mrow> <mo stretchy="false">(</mo> <msup> <mi>I</mi> <mrow> <mi>k</mi> <mo>+</mo> <mn>1</mn> </mrow> </msup> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. Investigating <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11587_2025_947_Article_IEq2.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="41" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mu (I^{k})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mo stretchy="false">(</mo> <msup> <mi>I</mi> <mi>k</mi> </msup> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> for small <i>k</i> has recently been of interest for many authors. In particular, some authors have constructed ideals with tiny powers, that is, <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11587_2025_947_Article_IEq6.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="117" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mu (I^{k+1})&lt;\mu (I^{k})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mrow> <mo stretchy="false">(</mo> <msup> <mi>I</mi> <mrow> <mi>k</mi> <mo>+</mo> <mn>1</mn> </mrow> </msup> <mo stretchy="false">)</mo> </mrow> <mo>&lt;</mo> <mi>μ</mi> <mrow> <mo stretchy="false">(</mo> <msup> <mi>I</mi> <mi>k</mi> </msup> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> for small <i>k</i>. In this paper, we give a shorter and simpler construction of monomial ideals <i>I</i> with tiny powers, up to any given power; that is, <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11587_2025_947_Article_IEq6.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="117" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mu (I^{k+1})&lt;\mu (I^{k})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mrow> <mo stretchy="false">(</mo> <msup> <mi>I</mi> <mrow> <mi>k</mi> <mo>+</mo> <mn>1</mn> </mrow> </msup> <mo stretchy="false">)</mo> </mrow> <mo>&lt;</mo> <mi>μ</mi> <mrow> <mo stretchy="false">(</mo> <msup> <mi>I</mi> <mi>k</mi> </msup> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> for all <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11587_2025_947_Article_IEq8.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">\(k\le l\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>≤</mo> <mi>l</mi> </mrow> </math></EquationSource> </InlineEquation> where <i>l</i> is any given positive integer <i>l</i>.</p>

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Monomial ideals with tiny powers: a simpler case

  • Omar Tout,
  • Ibrahim Al-Ayyoub

摘要

Let \(\mu (I)\) μ ( I ) denote the number of generators of the ideal I. It is well known that \(\mu (I^{k})\) μ ( I k ) is a polynomial for \(k\gg 0\) k 0 ; thus, \(\mu (I^{k})<\mu (I^{k+1})\) μ ( I k ) < μ ( I k + 1 ) . Investigating \(\mu (I^{k})\) μ ( I k ) for small k has recently been of interest for many authors. In particular, some authors have constructed ideals with tiny powers, that is, \(\mu (I^{k+1})<\mu (I^{k})\) μ ( I k + 1 ) < μ ( I k ) for small k. In this paper, we give a shorter and simpler construction of monomial ideals I with tiny powers, up to any given power; that is, \(\mu (I^{k+1})<\mu (I^{k})\) μ ( I k + 1 ) < μ ( I k ) for all \(k\le l\) k l where l is any given positive integer l.