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SEMILATTICES AND THE RAMSEY PROPERTY
Published online by Cambridge University Press: 22 December 2015
Abstract
We consider ${\cal S}$, the class of finite semilattices;
${\cal T}$, the class of finite treeable semilattices; and
${{\cal T}_m}$, the subclass of
${\cal T}$ which contains trees with branching bounded by m. We prove that
${\cal E}{\cal S}$, the class of finite lattices with linear extensions, is a Ramsey class. We calculate Ramsey degrees for structures in
${\cal S}$,
${\cal T}$, and
${{\cal T}_m}$. In addition to this we give a topological interpretation of our results and we apply our result to canonization of linear orderings on finite semilattices. In particular, we give an example of a Fraïssé class
${\cal K}$ which is not a Hrushovski class, and for which the automorphism group of the Fraïssé limit of
${\cal K}$ is not extremely amenable (with the infinite universal minimal flow) but is uniquely ergodic.
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- Copyright © The Association for Symbolic Logic 2015
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