Some examples of universal and generic partial orders

Universal Partial Words over Non-Binary Alphabets

Chen, Kitaev, Mütze, and Sun recently introduced the notion of universal partial words, a generalization of universal words and de Bruijn sequences. Universal partial words allow for a wild-card character $\diamond$, which is a placeholder for any letter in the alphabet. We settle and strengthen conjectures posed in the same paper where this notion was introduced. For non-binary alphabets, we show that universal partial words have periodic $\diamond$ structure and are cyclic, and we give number-theoretic conditions on the existence of universal partial words. In addition, we provide an explici…

Combinatorial Properties of Finite Models

We study countable embedding-universal and homomorphism-universal structures and unify results related to both of these notions. We show that many universal and ultrahomogeneous structures allow a concise description (called here a finite presentation). Extending classical work of Rado (for the random graph), we find a finite presentation for each of the following classes: homogeneous undirected graphs, homogeneous tournaments and homogeneous partially ordered sets. We also give a finite presentation of the rational Urysohn metric space and some homogeneous directed graphs. We survey well know…

图泛环：压缩及其与泛环的联系

Graph Universal Cycles: Compression and Connections to Universal Cycles

本文提出图泛部分环这一更紧凑的图类表示方法，并为带标签图、阈值图和置换图给出构造，同时揭示了其与泛环及压缩泛环的联系，还证明了置换图和无标签图上相关泛环形式的存在性。

通用部分环面

Universal partial tori

受通用部分循环进展启发，本文引入了通用部分环面和矩阵，通过计算方法发现并利用通用循环的一维变体构造了无穷多个此类结构。

Graph Relations and Constrained Homomorphism Partial Orders

We consider constrained variants of graph homomorphisms such as embeddings, monomorphisms, full homomorphisms, surjective homomorpshims, and locally constrained homomorphisms. We also introduce a new variation on this theme which derives from relations between graphs and is related to multihomomorphisms. This gives a generalization of surjective homomorphisms and naturally leads to notions of R-retractions, R-cores, and R-cocores of graphs. Both R-cores and R-cocores of graphs are unique up to isomorphism and can be computed in polynomial time. The theory of the graph homomorphism order is wel…

关于泛偏词

On universal partial words

本文首次系统研究泛偏词，即允许通配符的泛词，探讨其在不同通配符数量与位置下的存在性，并给出显式构造及计算机辅助示例。