Maria Chudnovsky, Cemil Dibek, Paul Seymour
A graph is strongly perfect if every induced subgraph H has a stable set that meets every nonempty maximal clique of H. The characterization of strongly perfect graphs by a set of forbidden induced subgraphs is not known. Here we provide several new minimal non-strongly-perfect graphs.
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We prove Ahlswede- Khachatrian conjecture. From this conjecture follows of several other conjectures including Manickam-Miklós-Singhi conjecture.
A graph is strongly perfect if every induced subgraph H has a stable set that meets every maximal clique of H. A graph is claw-free if no vertex has three pairwise non-adjacent neighbors. The characterization of claw-free graphs that are strongly perfect by a set of forbidden induced subgraphs was conjectured by Ravindra in 1990 and was proved by Wang in 2006. Here we give a shorter proof of this characterization.
The extremal 3-modular lattice $[\pm G_2(3)]_{14}$ with automorphism group $C_2 \times G_2(\F_3) $ is the unique dual strongly perfect lattice of dimension 14.
We call a finite undirected graph minimally k-matchable if it has at least k distinct perfect matchings but deleting any edge results in a graph which has not. An odd subdivision of some graph G is any graph obtained by replacing every edge of G by a path of odd length connecting its end vertices such that all these paths are internally disjoint. We prove that for every k>0 there exists a finite set of graphs S(k) such that every minimally k-matchable graph is isomorphic to a disjoint union of an odd subdivision of some graph from S(k) and any number of copies of the complete graph on two vert…
We classify the dual strongly perfect lattices in dimension 16. There are four pairs of such lattices, the famous Barnes-Wall lattice $Λ_{16}$, the extremal 5-modular lattice $N_{16}$, the odd Barnes-Wall lattice $O_{16}$ and its dual, and one pair of new lattices $Γ_{16}$ and its dual. The latter pair belongs to a new infinite series of dual strongly perfect lattices, the sandwiched Barnes-Wall lattices, described by the authors in a previous paper. An updated table of all known strongly perfect lattices up to dimension 26 is available in the catalogue of lattices.
In this paper we prove Ahlswede- Khachatrian conjecture~\cite{1} up to finite number of cases, which can be checked using modern computers. From this conjecture follows conjecture from~\cite{2} and Manickam-Miklós-Singhi conjecture. This paper is combined from papers~\cite{09},~\cite{08}.
Let $γ_g(G)$ and $γ_{tg}(G)$ be the game domination number and the total game domination number of a graph $G$, respectively. Then $G$ is $γ_g$-perfect (resp. $γ_{tg}$-perfect), if every induced subgraph $F$ of $G$ satisfies $γ_g(F)=γ(F)$ (resp. $γ_{tg}(F)=γ_t(F)$). A recursive characterization of $γ_g$-perfect graphs is derived. The characterization yields a polynomial recognition algorithm for $γ_g$-perfect graphs. It is proved that every minimally $γ_g$-imperfect graph has domination number $2$. All minimally $γ_g$-imperfect triangle-free graphs are determined. It is also proved that $γ_{tg…
Some properties of minimally nonperfectly divisible graphs
本文研究了极小非完美可除图的性质，证明了特定类别的极小非完美可除图不包含团割集，回答了相关问题。
We prove that a triangulation of the projective plane is (strongly) $t$-perfect if and only if it is perfect and contains no $K_4$.
This is a not-to-be-journal-published paper, aimed to serve as reference. It is a summary of the main ideas on the topic appearing in the title, and an opportunity to state correctly the main conjecture in the field.
Strongly regular and strongly walk-regular graphs that admit perfect state transfer
研究强正则图和强行走正则图中允许完美态转移的图，通过谱分析确定其结构特征。
The problem of leaders location plays an important role in the controllability of undirected graphs.The concept of minimal perfect critical vertex set is introduced by drawing support from the eigenvector of Laplace matrix. Using the notion of minimal perfect critical vertex set, the problem of finding the minimum number of controllable leader vertices is transformed into the problem of finding all minimal perfect critical vertex sets. Some necessary and sufficient conditions for special minimal perfect critical vertex sets are provided, such as minimal perfect critical 2 vertex set, and minim…
Pure minimal injective resolutions and perfect modules for lattices
本文研究了分布格子的纯极小投射化解析条件，并分类了完美反链模，揭示了格子理论与同调代数之间的联系。
On minimal nonperfectly divisible fork-free graphs
研究无叉图的完全可分性，证明其与无爪图的完全可分性等价，并针对特定的\(F\)，证明（无叉，\(F\)）-自由图\(G\)完全可分且\(\chi(G)\leq \binom{\omega(G)+1}{2}\)。
Counterexamples to conjectures on strong maximality and minimality
本文针对无限图和超图中强极大与强极小结构的猜想，构造3-一致超图等反例，解决了多位学者提出的相关猜想与问题。
On the structure of perfectly divisible graphs
本文研究完美可分图的结构，证明不含P₅的极小非完美可分图无团割集，可重立相关图类的完美可分性定理，并指出识别完美可分图是NP难的。
An {\sf oriented perfect path double cover} ($\rm OPPDC$) of a graph $G$ is a collection of directed paths in the symmetric orientation $G_s$ of $G$ such that each edge of $G_s$ lies in exactly one of the paths and each vertex of $G$ appears just once as a beginning and just once as an end of a path. Maxov{á} and Ne{š}et{ř}il (Discrete Math. 276 (2004) 287-294) conjectured that every graph except two complete graphs $K_3$ and $K_5$ has an $\rm OPPDC$ and they proved that the minimum degree of the minimal counterexample to this conjecture is at least four. In this paper, among some other result…
Kloks, Kratsch, and Spinrad showed how treewidth and minimum-fill, NP-hard combinatorial optimization problems related to minimal triangulations, are broken into subproblems by block subgraphs defined by minimal separators. These ideas were expanded on by Bouchitté and Todinca, who used potential maximal cliques to solve these problems using a dynamic programming approach in time polynomial in the number of minimal separators of a graph. It is known that solutions to the perfect phylogeny problem, maximum compatibility problem, and unique perfect phylogeny problem are characterized by minimal …
The minimal nonplanar strong digraphs
本文将 Kuratowski 定理推广到有向图，刻画了在子有向图包含关系下最小的强连通非平面、非外平面及非串并联有向图。
The spectral radii and extremal graphs of two types of minimal graphs
本文通过耳分解和边交换技术，确定了极小匹配覆盖双图和极小因子临界图的最大谱半径并刻画了极值图。
New series of $2^{2m}$-dimensional universally strongly perfect lattices $Λ_I $ and $Γ_J $ are constructed with $$2BW_{2m} ^{\#} \subseteq Γ_J \subseteq BW_{2m} \subseteq Λ_I \subseteq BW _{2m}^{\#} .$$ The lattices are found by restricting the spin representations of the automorphism group of the Barnes-Wall lattice to its subgroup ${\mathcal U}_m:={\mathcal C}_m (4^H_{\bf 1}) $. The group ${\mathcal U}_m$ is the Clifford-Weil group associated to the Hermitian self-dual codes over ${\bf F} _4$ containing ${\bf 1}$, so the ring of polynomial invariants of ${\mathcal U}_m$ is spanned by the gen…
Perfect codes in 2-valent Cayley digraphs on abelian groups
研究阿贝尔群上强连通2价Cayley有向图的完美码问题，完成图的分类并完全确定其所有完美码。
We show that the probability that a random graph $G\sim G(n,p)$ contains no Hamilton cycle is $(1+o(1))Pr(δ(G) < 2)$ for all values of $p = p(n)$. We also prove an analogous result for perfect matchings.
A graph property P is strongly testable if for every fixed ε>0 there is a one-sided ε-tester for P whose query complexity is bounded by a function of ε. In classifying the strongly testable graph properties, the first author and Shapira showed that any hereditary graph property (such as P the family of perfect graphs) is strongly testable. A property is easily testable if it is strongly testable with query complexity bounded by a polynomial function of ε^{-1}, and otherwise it is hard. One of our main results shows that testing perfectness is hard. The proof shows that testing perfectness is a…
A graph G is perfect if for every induced subgraph H, the chromatic number of H equals the size of the largest complete subgraph of H, and G is Berge if no induced subgraph of G is an odd cycle of length at least 5 or the complement of one. The "strong perfect graph conjecture" (Berge, 1961) asserts that a graph is perfect if and only if it is Berge. A stronger conjecture was made recently by Conforti, Cornuejols and Vuskovic -- that every Berge graph either falls into one of a few basic classes, or it has a kind of separation that cannot occur in a minimal imperfect graph. In this paper we pr…
Koolen et al. showed that if a connected graph with smallest eigenvalue at least $-3$ has large minimal valency, then it is $2$-integrable. In this paper, we will prove that a lower bound for the minimal valency is 166.
We introduce a uniform method of proof for the following results. For {\em each} of the following conditions, there are $2^{\aleph_0}$ families of Steiner systems, satisfying that condition: i) Theorem~2.2.4: (extending \cite{Chicoetal}) each Steiner triple system is $\infty$-sparse and has a uniform but not perfect path graph; ii) (Theorem~5.4.2: (extending \cite{CameronWebb}) each Steiner $k$-system (for $k=p^n$) is $2$-transitive and has a uniform path graph (infinite cycles only); iii) Theorem~2.1.5: (extending \cite{Fujiwaramitre}, each is anti-Pasch (anti-mitre); iv) Theorem~3.6 has an e…
The minimum degree of minimal 2-extendable claw-free graphs
针对极小 $k$-可扩无爪图的度下界问题，本文证明极小 2-可扩无爪图的最小度只能是 4 或 5。
An edge subset $S$ of a connected graph $G$ is called an anti-Kekulé set if $G-S$ is connected and has no perfect matching. We can see that a connected graph $G$ has no anti-Kekulé set if and only if each spanning tree of $G$ has a perfect matching. In this paper, by applying Tutte's 1-factor theorem and structure of minimally 2-connected graphs, we characterize all graphs whose each spanning tree has a perfect matching In addition, we show that if $G$ is a connected graph of order $2n$ for a positive integer $n\geq 4$ and size $m$ whose each spanning tree has a perfect matching, then $m\leq \…
The anti-forcing number of a perfect matching $M$ of a graph $G$ is the minimal number of edges not in $M$ whose removal to make $M$ as a unique perfect matching of the resulting graph. The set of anti-forcing numbers of all perfect matchings of $G$ is the anti-forcing spectrum of $G$. In this paper, we characterize the plane elementary bipartite graph whose minimum anti-forcing number is one. We show that the maximum anti-forcing number of a graph is at most its cyclomatic number. In particular, we characterize the graphs with the maximum anti-forcing number achieving the upper bound, such ex…
An infinite family of minimally nonperfectly divisible graphs with a bisimplicial vertex
反驳Hoàng关于极小非完全可分图不能含双单纯顶点的猜想，构造反例图，基于带根图用强制机制，其无完美划分但真诱导子图可分，还对Hu、Xu和Zhuang的规定顶点问题给出否定回答。
We prove a generalizations of the Elekes-Szabó theorem for relations definable in strongly minimal structures that are interpretable in distal structures.
Inspired by applications of perfect graphs in combinatorial optimization, Chvátal defined t-perfect graphs in 1970s. The long efforts of characterizing t-perfect graphs started immediately, but embarrassingly, even a working conjecture on it is still missing after nearly 50 years. Unlike perfect graphs, t-perfect graphs are not closed under substitution or complementation. A full characterization of t-perfection with respect to substitution has been obtained by Benchetrit in his Ph.D. thesis. Through the present work we attempt to understand t-perfection with respect to complementation. In par…
In an attempt to understanding the complexity of the independent set problem, Chv{á}tal defined t-perfect graphs. While a full characterization of this class is still at large, progress has been achieved for claw-free graphs [Bruhn and Stein, Math.\ Program.\ 2012] and $P_{5}$-free graphs [Bruhn and Fuchs, SIAM J.\ Discrete Math.\ 2017]. We take one more step to characterize fork-free t-perfect graphs, and show that they are strongly t-perfect and three-colorable. We also present polynomial-time algorithms for recognizing and coloring these graphs.
On strongly minimal asymptotic bases of order $h$ generated by powers of $2$
本文针对非负整数集的h分划，给出由各分划子集对应的2的幂有限和集的并构成h阶强极小渐近基的充要条件，解答了Nathanson1988年提出的相关问题。
The perfect phylogeny problem is a classic problem in computational biology, where we seek an unrooted phylogeny that is compatible with a set of qualitative characters. Such a tree exists precisely when an intersection graph associated with the character set, called the partition intersection graph, can be triangulated using a restricted set of fill edges. Semple and Steel used the partition intersection graph to characterize when a character set has a unique perfect phylogeny. Bordewich, Huber, and Semple showed how to use the partition intersection graph to find a maximum compatible set of …
Based upon a previous work of Manjunath and Sturmfels for a finite, complete, undirected graph, and a refined algorithm by Eröcal, Motsak, Schreyer and Steenpaß for computing syzygies, we display a free resolution of the lattice ideal associated to a finite, strongly connected, weighted, directed graph. Moreover, the resolution is minimal precisely when the digraph is strongly complete.
Finding Spanning Trees with Perfect Matchings
该研究探讨含完美匹配的最小权重生成树问题的可处理性，给出特定图与边权条件下的贪心算法，证明多类场景下该问题及强平衡生成树判定问题为NP难。
Complexity of polytope diameters via perfect matchings
本文证明计算多胞体电路直径是强NP-hard问题，通过二部图完美匹配多胞体直径的NP-hard性实现，并给出单调直径的图论描述。
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