<p>A well known theorem proved in 1960 by Browder states that the set of fixed points of a family of continuous functions <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1259_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="97" /> </InlineMediaObject> <EquationSource Format="TEX">\(f_{p}:C\longrightarrow C\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>f</mi> <mi>p</mi> </msub> <mo>:</mo> <mi>C</mi> <mo stretchy="false">⟶</mo> <mi>C</mi> </mrow> </math></EquationSource> </InlineEquation>, <i>C</i> being a compact and convex subset of <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1259_Article_IEq2.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="20" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathbb {R}^{d}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mi>d</mi> </msup> </math></EquationSource> </InlineEquation>, depending continuously on a parameter <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1259_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="64" /> </InlineMediaObject> <EquationSource Format="TEX">\(p\in [0,1]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>p</mi> <mo>∈</mo> <mo stretchy="false">[</mo> <mn>0</mn> <mo>,</mo> <mn>1</mn> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation>, i.e. the set <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1259_Article_IEq4.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="286" /> </InlineMediaObject> <EquationSource Format="TEX">\(C_{f}:=\{(p,x)\in [0,1]\times C: f(p,x)=x\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>C</mi> <mi>f</mi> </msub> <mo>:</mo> <mo>=</mo> <mrow> <mo stretchy="false">{</mo> <mrow> <mo stretchy="false">(</mo> <mi>p</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>∈</mo> <mrow> <mo stretchy="false">[</mo> <mn>0</mn> <mo>,</mo> <mn>1</mn> <mo stretchy="false">]</mo> </mrow> <mo>×</mo> <mi>C</mi> <mo>:</mo> <mi>f</mi> <mrow> <mo stretchy="false">(</mo> <mi>p</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mi>x</mi> <mo stretchy="false">}</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, has a connected component whose projection on the first coordinate is [0,&#xa0;1]. The same result remains true if <i>C</i> is a closed and convex subset of a Banach space and <i>f</i> is compact. In the present paper, by using the so-called degree of nondensifiability (DND), we introduce a new class of mappings called parametric DND-condensing (which is a generalization of the class of compact mappings) and prove a generalization of Browder’s theorem. Moreover, in the proposed generalization, we can replace the parameter space [0,&#xa0;1] by an arbitrary Peano Continuum of a Banach space.</p>

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A generalization of Browder’s Theorem to parametric DND-condensing mappings

  • Gonzalo García

摘要

A well known theorem proved in 1960 by Browder states that the set of fixed points of a family of continuous functions \(f_{p}:C\longrightarrow C\) f p : C C , C being a compact and convex subset of \(\mathbb {R}^{d}\) R d , depending continuously on a parameter \(p\in [0,1]\) p [ 0 , 1 ] , i.e. the set \(C_{f}:=\{(p,x)\in [0,1]\times C: f(p,x)=x\}\) C f : = { ( p , x ) [ 0 , 1 ] × C : f ( p , x ) = x } , has a connected component whose projection on the first coordinate is [0, 1]. The same result remains true if C is a closed and convex subset of a Banach space and f is compact. In the present paper, by using the so-called degree of nondensifiability (DND), we introduce a new class of mappings called parametric DND-condensing (which is a generalization of the class of compact mappings) and prove a generalization of Browder’s theorem. Moreover, in the proposed generalization, we can replace the parameter space [0, 1] by an arbitrary Peano Continuum of a Banach space.