<p>We study the homomorphism-homogeneity of normal bands <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="233_2025_10517_Article_IEq1.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="124" /> </InlineMediaObject> <EquationSource Format="TEX">\(B=[Y;B_{\alpha };\psi _{\alpha ,\beta }]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>B</mi> <mo>=</mo> <mo stretchy="false">[</mo> <mi>Y</mi> <mo>;</mo> <msub> <mi>B</mi> <mi>α</mi> </msub> <mo>;</mo> <msub> <mi>ψ</mi> <mrow> <mi>α</mi> <mo>,</mo> <mi>β</mi> </mrow> </msub> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> (that is, a spined product of a left normal band <i>L</i> and a right normal band <i>R</i>). We show that if <i>B</i> is homomorphism-homogeneous, then one of the following conditions holds: (i) <i>B</i> is image-trivial; (ii) <i>B</i> is surjective; (iii) <i>L</i> is image-trivial (resp. surjective) and <i>R</i> is surjective (resp. image-trivial). Furthermore, we show that any iso-normal band is homomorphism-homogeneous if and only if its structure semilattice is homomorphism-homogeneous. Consequently, a non-image-trivial injective normal band <i>B</i> is homomorphism-homogeneous if and only if <i>B</i> is iso-normal and its structure semilattice is homomorphism-homogeneous. We also classify homomorphism-homogeneous image-trivial normal bands whose structure semilattices are trees. It is shown that any such normal band is homomorphism-homogeneous if and only if it has trivial minimum-collapsing, which is a restriction on the size of the <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="233_2025_10517_Article_IEq2.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="23" /> </InlineMediaObject> <EquationSource Format="TEX">\(B_\alpha \)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>B</mi> <mi>α</mi> </msub> </math></EquationSource> </InlineEquation>. Consequently, an image-trivial normal band in which <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="233_2025_10517_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="23" /> </InlineMediaObject> <EquationSource Format="TEX">\(R_\alpha \)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>R</mi> <mi>α</mi> </msub> </math></EquationSource> </InlineEquation> is non-trivial for all non-minimal elements <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="233_2025_10517_Article_IEq4.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="46" /> </InlineMediaObject> <EquationSource Format="TEX">\(\alpha \in Y\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>α</mi> <mo>∈</mo> <mi>Y</mi> </mrow> </math></EquationSource> </InlineEquation> is homomorphism-homogeneous if and only if <i>Y</i> is a tree and <i>B</i> has trivial minimum-collapsing.</p>

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Homomorphism-homogeneous normal bands

  • Wenjie Yang,
  • Dandan Yang

摘要

We study the homomorphism-homogeneity of normal bands \(B=[Y;B_{\alpha };\psi _{\alpha ,\beta }]\) B = [ Y ; B α ; ψ α , β ] (that is, a spined product of a left normal band L and a right normal band R). We show that if B is homomorphism-homogeneous, then one of the following conditions holds: (i) B is image-trivial; (ii) B is surjective; (iii) L is image-trivial (resp. surjective) and R is surjective (resp. image-trivial). Furthermore, we show that any iso-normal band is homomorphism-homogeneous if and only if its structure semilattice is homomorphism-homogeneous. Consequently, a non-image-trivial injective normal band B is homomorphism-homogeneous if and only if B is iso-normal and its structure semilattice is homomorphism-homogeneous. We also classify homomorphism-homogeneous image-trivial normal bands whose structure semilattices are trees. It is shown that any such normal band is homomorphism-homogeneous if and only if it has trivial minimum-collapsing, which is a restriction on the size of the \(B_\alpha \) B α . Consequently, an image-trivial normal band in which \(R_\alpha \) R α is non-trivial for all non-minimal elements \(\alpha \in Y\) α Y is homomorphism-homogeneous if and only if Y is a tree and B has trivial minimum-collapsing.