<p>We introduce a generator-counting refinement of algebrability for abelian <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(C^*\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>C</mi> <mo>∗</mo> </msup> </math></EquationSource> </InlineEquation>-algebras and related Banach algebras. Given an abelian <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(C^*\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>C</mi> <mo>∗</mo> </msup> </math></EquationSource> </InlineEquation>-algebra <i>A</i>, we define <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\((C^*)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <msup> <mi>C</mi> <mo>∗</mo> </msup> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>-genalgebrability in terms of the minimal possible cardinality of a generating set, encoded by the invariants <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\({{\,\textrm{gen}\,}}_{C^*}(A)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mrow> <mspace width="0.166667em" /> <mtext>gen</mtext> <mspace width="0.166667em" /> </mrow> <msup> <mi>C</mi> <mo>∗</mo> </msup> </msub> <mrow> <mo stretchy="false">(</mo> <mi>A</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\({{\,\textrm{gen}\,}}(A)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mspace width="0.166667em" /> <mtext>gen</mtext> <mspace width="0.166667em" /> </mrow> <mo stretchy="false">(</mo> <mi>A</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>. Using compact multipliers and the ideal <i>K</i>(<i>A</i>) of compact elements, we develop embedding results into <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\ell _\infty \)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>ℓ</mi> <mi>∞</mi> </msub> </math></EquationSource> </InlineEquation> whose ranges avoid <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(c_0\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>c</mi> <mn>0</mn> </msub> </math></EquationSource> </InlineEquation> (except for the zero vector), and we obtain a universal <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\((\ell _\infty \setminus c_0)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <msub> <mi>ℓ</mi> <mi>∞</mi> </msub> <mo lspace="0.15em" rspace="0.15em" stretchy="false">\</mo> <msub> <mi>c</mi> <mn>0</mn> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>-embeddability phenomenon under the assumption <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(K(A)=\{0\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>K</mi> <mo stretchy="false">(</mo> <mi>A</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mo stretchy="false">{</mo> <mn>0</mn> <mo stretchy="false">}</mo> </mrow> </math></EquationSource> </InlineEquation>. As an application, we construct a <InlineEquation ID="IEq14"> <EquationSource Format="TEX">\({\phantom {a}}^*\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mphantom> <mi>a</mi> </mphantom> </mrow> <mo>∗</mo> </msup> </math></EquationSource> </InlineEquation>-isomorphic copy of <InlineEquation ID="IEq15"> <EquationSource Format="TEX">\(\ell _\infty \)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>ℓ</mi> <mi>∞</mi> </msub> </math></EquationSource> </InlineEquation> inside <InlineEquation ID="IEq16"> <EquationSource Format="TEX">\((\ell _\infty \setminus c_0)\cup \{0\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo stretchy="false">(</mo> <msub> <mi>ℓ</mi> <mi>∞</mi> </msub> <mo lspace="0.15em" rspace="0.15em" stretchy="false">\</mo> <msub> <mi>c</mi> <mn>0</mn> </msub> <mo stretchy="false">)</mo> </mrow> <mo>∪</mo> <mrow> <mo stretchy="false">{</mo> <mn>0</mn> <mo stretchy="false">}</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> and transfer the results to Calkin-type settings such as <InlineEquation ID="IEq17"> <EquationSource Format="TEX">\((B(\ell _2)\setminus \mathcal {K}(\ell _2))\cup \{0\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo stretchy="false">(</mo> <mi>B</mi> <mrow> <mo stretchy="false">(</mo> <msub> <mi>ℓ</mi> <mn>2</mn> </msub> <mo stretchy="false">)</mo> </mrow> <mo lspace="0.15em" rspace="0.15em" stretchy="false">\</mo> <mi mathvariant="script">K</mi> <mrow> <mo stretchy="false">(</mo> <msub> <mi>ℓ</mi> <mn>2</mn> </msub> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">)</mo> </mrow> <mo>∪</mo> <mrow> <mo stretchy="false">{</mo> <mn>0</mn> <mo stretchy="false">}</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> and their unitizations. We also establish a generator-counting theorem for abelian <InlineEquation ID="IEq18"> <EquationSource Format="TEX">\(C^*\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>C</mi> <mo>∗</mo> </msup> </math></EquationSource> </InlineEquation>-algebras: <InlineEquation ID="IEq19"> <EquationSource Format="TEX">\({{\,\textrm{gen}\,}}_{C^*}(A)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mrow> <mspace width="0.166667em" /> <mtext>gen</mtext> <mspace width="0.166667em" /> </mrow> <msup> <mi>C</mi> <mo>∗</mo> </msup> </msub> <mrow> <mo stretchy="false">(</mo> <mi>A</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> equals the smallest cardinal <i>n</i> for which the spectrum <InlineEquation ID="IEq20"> <EquationSource Format="TEX">\(\Delta (A)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <mo stretchy="false">(</mo> <mi>A</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> embeds into <InlineEquation ID="IEq21"> <EquationSource Format="TEX">\(\mathbb {R}^n\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mi>n</mi> </msup> </math></EquationSource> </InlineEquation>, and we derive topological formulas for <InlineEquation ID="IEq22"> <EquationSource Format="TEX">\({{\,\textrm{gen}\,}}_{C^*}(A)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mrow> <mspace width="0.166667em" /> <mtext>gen</mtext> <mspace width="0.166667em" /> </mrow> <msup> <mi>C</mi> <mo>∗</mo> </msup> </msub> <mrow> <mo stretchy="false">(</mo> <mi>A</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> in the non-finitely generated case. Finally, we provide a complete classification of the pairs <InlineEquation ID="IEq23"> <EquationSource Format="TEX">\((d,\kappa )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mo>,</mo> <mi>κ</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> for which <InlineEquation ID="IEq24"> <EquationSource Format="TEX">\((\ell _\infty \setminus c_0)\cup \{0\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo stretchy="false">(</mo> <msub> <mi>ℓ</mi> <mi>∞</mi> </msub> <mo lspace="0.15em" rspace="0.15em" stretchy="false">\</mo> <msub> <mi>c</mi> <mn>0</mn> </msub> <mo stretchy="false">)</mo> </mrow> <mo>∪</mo> <mrow> <mo stretchy="false">{</mo> <mn>0</mn> <mo stretchy="false">}</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> is <InlineEquation ID="IEq25"> <EquationSource Format="TEX">\((d,\kappa )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mo>,</mo> <mi>κ</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>-<InlineEquation ID="IEq26"> <EquationSource Format="TEX">\((C^*)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <msup> <mi>C</mi> <mo>∗</mo> </msup> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>-genalgebrable, and we discuss the connection with classical algebrability.</p>

错误:搜索内容不能为空,请输入英文关键词
错误:关键词超出字数限制,请精简
高级检索

Applications of compact multipliers to algebrability of \((\ell _{\infty }\setminus c_0)\cup \{0\}\) and \((B(\ell _2)\setminus K(\ell _2))\cup \{ 0\}\)

  • W. Franca,
  • Jorge J. Garcés

摘要

We introduce a generator-counting refinement of algebrability for abelian \(C^*\) C -algebras and related Banach algebras. Given an abelian \(C^*\) C -algebra A, we define \((C^*)\) ( C ) -genalgebrability in terms of the minimal possible cardinality of a generating set, encoded by the invariants \({{\,\textrm{gen}\,}}_{C^*}(A)\) gen C ( A ) and \({{\,\textrm{gen}\,}}(A)\) gen ( A ) . Using compact multipliers and the ideal K(A) of compact elements, we develop embedding results into \(\ell _\infty \) whose ranges avoid \(c_0\) c 0 (except for the zero vector), and we obtain a universal \((\ell _\infty \setminus c_0)\) ( \ c 0 ) -embeddability phenomenon under the assumption \(K(A)=\{0\}\) K ( A ) = { 0 } . As an application, we construct a \({\phantom {a}}^*\) a -isomorphic copy of \(\ell _\infty \) inside \((\ell _\infty \setminus c_0)\cup \{0\}\) ( \ c 0 ) { 0 } and transfer the results to Calkin-type settings such as \((B(\ell _2)\setminus \mathcal {K}(\ell _2))\cup \{0\}\) ( B ( 2 ) \ K ( 2 ) ) { 0 } and their unitizations. We also establish a generator-counting theorem for abelian \(C^*\) C -algebras: \({{\,\textrm{gen}\,}}_{C^*}(A)\) gen C ( A ) equals the smallest cardinal n for which the spectrum \(\Delta (A)\) Δ ( A ) embeds into \(\mathbb {R}^n\) R n , and we derive topological formulas for \({{\,\textrm{gen}\,}}_{C^*}(A)\) gen C ( A ) in the non-finitely generated case. Finally, we provide a complete classification of the pairs \((d,\kappa )\) ( d , κ ) for which \((\ell _\infty \setminus c_0)\cup \{0\}\) ( \ c 0 ) { 0 } is \((d,\kappa )\) ( d , κ ) - \((C^*)\) ( C ) -genalgebrable, and we discuss the connection with classical algebrability.