<p>Let (<i>X</i>,&#xa0;0) be the germ of an equidimensional analytic set in <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13163_2025_522_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="48" /> </InlineMediaObject> <EquationSource Format="TEX">\(({\mathbb {C}}^n,0)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <msup> <mrow> <mi mathvariant="double-struck">C</mi> </mrow> <mi>n</mi> </msup> <mo>,</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13163_2025_522_Article_IEq2.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="133" /> </InlineMediaObject> <EquationSource Format="TEX">\(F=(f,g_1,\ldots ,g_p)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>F</mi> <mo>=</mo> <mo stretchy="false">(</mo> <mi>f</mi> <mo>,</mo> <msub> <mi>g</mi> <mn>1</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>g</mi> <mi>p</mi> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> a map-germ into <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13163_2025_522_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="33" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathbb {C}}^{p+1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="double-struck">C</mi> </mrow> <mrow> <mi>p</mi> <mo>+</mo> <mn>1</mn> </mrow> </msup> </math></EquationSource> </InlineEquation> defined on <i>X</i>. In this work, we investigate topological invariants associated to the pair (<i>F</i>,&#xa0;<i>X</i>),&#xa0; among them, the Euler obstruction of <i>F</i>,&#xa0; <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13163_2025_522_Article_IEq4.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="72" /> </InlineMediaObject> <EquationSource Format="TEX">\(Eu_{F,X}(0),\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>E</mi> <msub> <mi>u</mi> <mrow> <mi>F</mi> <mo>,</mo> <mi>X</mi> </mrow> </msub> <mrow> <mo stretchy="false">(</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> and under convenient assumptions, the Chern obstruction of families of differential forms associated to <i>F</i>. The topological information provided by these invariants is useful, although difficult to calculate. The aim of the paper is to introduce the Bruce-Roberts and the relative Bruce-Roberts numbers as useful algebraic tools to capture the topological information given by the Euler obstruction and the Chern obstruction. Closed formulas are given when <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13163_2025_522_Article_IEq5.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="204" /> </InlineMediaObject> <EquationSource Format="TEX">\(X,\, X\cap F^{-1}(0),\, X\cap G^{-1}(0)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>X</mi> <mo>,</mo> <mspace width="0.166667em" /> <mi>X</mi> <mo>∩</mo> <msup> <mi>F</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mrow> <mo stretchy="false">(</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> <mspace width="0.166667em" /> <mi>X</mi> <mo>∩</mo> <msup> <mi>G</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mrow> <mo stretchy="false">(</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> are ICIS, for <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13163_2025_522_Article_IEq6.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="116" /> </InlineMediaObject> <EquationSource Format="TEX">\(G=(g_1,\ldots ,g_p)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>G</mi> <mo>=</mo> <mo stretchy="false">(</mo> <msub> <mi>g</mi> <mn>1</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>g</mi> <mi>p</mi> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>. In the last section, for a 2-dimensional ICIS <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13163_2025_522_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="118" /> </InlineMediaObject> <EquationSource Format="TEX">\((X,0) \subset ({\mathbb {C}}^n,0),\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo>,</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> <mo>⊂</mo> <mrow> <mo stretchy="false">(</mo> <msup> <mrow> <mi mathvariant="double-struck">C</mi> </mrow> <mi>n</mi> </msup> <mo>,</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> we apply our results to give an alternative description for the number of cusps <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13163_2025_522_Article_IEq8.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="47" /> </InlineMediaObject> <EquationSource Format="TEX">\(c(f|_X)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>c</mi> <mo stretchy="false">(</mo> <mi>f</mi> <msub> <mo stretchy="false">|</mo> <mi>X</mi> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> of a stabilization of an <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13163_2025_522_Article_IEq9.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathcal {A}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">A</mi> </math></EquationSource> </InlineEquation>-finite map-germ <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13163_2025_522_Article_IEq10.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="216" /> </InlineMediaObject> <EquationSource Format="TEX">\(f=(f_1, f_2): (X,0) \rightarrow ({\mathbb {C}}^2,0).\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mo>=</mo> <mrow> <mo stretchy="false">(</mo> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo>,</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">→</mo> <mrow> <mo stretchy="false">(</mo> <msup> <mrow> <mi mathvariant="double-struck">C</mi> </mrow> <mn>2</mn> </msup> <mo>,</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation> A formula for <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13163_2025_522_Article_IEq8.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="47" /> </InlineMediaObject> <EquationSource Format="TEX">\(c(f|_X)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>c</mi> <mo stretchy="false">(</mo> <mi>f</mi> <msub> <mo stretchy="false">|</mo> <mi>X</mi> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> was first given in Massey (Topology 35(4):969-1003, 1996).</p>

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Relative Bruce-Roberts number and Chern obstruction

  • Bárbara K. Lima Pereira,
  • Maria Aparecida Soares Ruas,
  • Hellen Santana

摘要

Let (X, 0) be the germ of an equidimensional analytic set in \(({\mathbb {C}}^n,0)\) ( C n , 0 ) and \(F=(f,g_1,\ldots ,g_p)\) F = ( f , g 1 , , g p ) a map-germ into \({\mathbb {C}}^{p+1}\) C p + 1 defined on X. In this work, we investigate topological invariants associated to the pair (FX),  among them, the Euler obstruction of F \(Eu_{F,X}(0),\) E u F , X ( 0 ) , and under convenient assumptions, the Chern obstruction of families of differential forms associated to F. The topological information provided by these invariants is useful, although difficult to calculate. The aim of the paper is to introduce the Bruce-Roberts and the relative Bruce-Roberts numbers as useful algebraic tools to capture the topological information given by the Euler obstruction and the Chern obstruction. Closed formulas are given when \(X,\, X\cap F^{-1}(0),\, X\cap G^{-1}(0)\) X , X F - 1 ( 0 ) , X G - 1 ( 0 ) are ICIS, for \(G=(g_1,\ldots ,g_p)\) G = ( g 1 , , g p ) . In the last section, for a 2-dimensional ICIS \((X,0) \subset ({\mathbb {C}}^n,0),\) ( X , 0 ) ( C n , 0 ) , we apply our results to give an alternative description for the number of cusps \(c(f|_X)\) c ( f | X ) of a stabilization of an \({\mathcal {A}}\) A -finite map-germ \(f=(f_1, f_2): (X,0) \rightarrow ({\mathbb {C}}^2,0).\) f = ( f 1 , f 2 ) : ( X , 0 ) ( C 2 , 0 ) . A formula for \(c(f|_X)\) c ( f | X ) was first given in Massey (Topology 35(4):969-1003, 1996).