arXiv subjects
Publications and source records attributed to John K Truss.
We give a flexible method for constructing a wide variety of limits of betweenness relations. This unifies work of Adeleke, who constructed a Jordan group preserving a limit of betweenness relations, and Bhattacharjee and Macpherson who gave an alternative method using a Frassé-type construction. A key ingredient in their work is the notion of a tree of B-sets. We employ this, and extend its use to a wider class of examples.
In this paper, we define the action of $M$, the monoid of embeddings of $({\mathbb Q}, \le)$, on $\mathbb Q$, in the monoid $(M, \circ)$. That is, we show that $\mathbb Q$ itself can be interpreted in $(M, \circ)$, and in addition, so can the action of $M$ on $\mathbb Q$. This is extended to the monoid $E$ of all endomorphisms of $({\mathbb Q}, \le)$.
We extend results from an earlier paper giving reconstruction results for the endomorphism monoid of the rational numbers under the strict and reflexive relations to the first order reducts of the rationals and the corresponding polymorphism clones. We also give some similar results about the coloured rationals.
Two structures A and B are n-equivalent if player II has a winning strategy in the n-move Ehrenfeucht-Fraisse game on A and B. We extend earlier results about n-equivalence for finite coloured linear orders, describing an algorithm for reducing to canonical form under 2-equivalence, and concentrating on the cases of 2 and 3 moves.
We show how to reconstruct the topology on the monoid of endomorphisms of the rational numbers under the strict or reflexive order relation, and the polymorphism clone of the rational numbers under the reflexive relation. In addition we show how automatic homeomorphicity results can be lifted to polymorphism clones generated by monoids.
We classify the countable homogeneous coloured multipartite graphs with any finite number of parts. By Fraisse's Theorem this amounts to classifying the families F of pairwise non-embeddable finite coloured multipartite graphs for which the class Forb(F) of multipartite graphs which forbid these is an amalgamation class. We show that once we understand such families F in the quadripartite case, things do not become any more complicated for larger numbers of parts.