ترغب بنشر مسار تعليمي؟ اضغط هنا

On a recolouring version of Hadwigers conjecture

153   0   0.0 ( 0 )
 نشر من قبل Cl\\'ement Legrand-Duchesne
 تاريخ النشر 2021
  مجال البحث الهندسة المعلوماتية
والبحث باللغة English




اسأل ChatGPT حول البحث

We prove that for any $varepsilon>0$, for any large enough $t$, there is a graph $G$ that admits no $K_t$-minor but admits a $(frac32-varepsilon)t$-colouring that is frozen with respect to Kempe changes, i.e. any two colour classes induce a connected component. This disproves three conjectures of Las Vergnas and Meyniel from 1981.


قيم البحث

اقرأ أيضاً

131 - Yan Wang 2021
Hadwiger conjectured in 1943 that for every integer $t ge 1$, every graph with no $K_t$ minor is $(t-1)$-colorable. Kostochka, and independently Thomason, proved every graph with no $K_t$ minor is $O(t(log t)^{1/2})$-colorable. Recently, Postle impro ved it to $O(t (log log t)^6)$-colorable. In this paper, we show that every graph with no $K_t$ minor is $O(t (log log t)^{5})$-colorable.
Hadwigers conjecture is one of the most important and long-standing conjectures in graph theory. Reed and Seymour showed in 2004 that Hadwigers conjecture is true for line graphs. We investigate this conjecture on the closely related class of total g raphs. The total graph of $G$, denoted by $T(G)$, is defined on the vertex set $V(G)sqcup E(G)$ with $c_1,c_2in V(G)sqcup E(G)$ adjacent whenever $c_1$ and $c_2$ are adjacent to or incident on each other in $G$. We first show that there exists a constant $C$ such that, if the connectivity of $G$ is at least $C$, then Hadwigers conjecture is true for $T(G)$. The total chromatic number $chi(G)$ of a graph $G$ is defined to be equal to the chromatic number of its total graph. That is, $chi(G)=chi(T(G))$. Another well-known conjecture in graph theory, the total coloring conjecture or TCC, states that for every graph $G$, $chi(G)leqDelta(G)+2$, where $Delta(G)$ is the maximum degree of $G$. We show that if a weaker version of the total coloring conjecture (weak TCC) namely, $chi(G)leqDelta(G)+3$, is true for a class of graphs $mathcal{F}$ that is closed under the operation of taking subgraphs, then Hadwigers conjecture is true for the class of total graphs of graphs in $mathcal{F}$. This motivated us to look for classes of graphs that satisfy weak TCC. It may be noted that a complete proof of TCC for even 4-colorable graphs (in fact even for planar graphs) has remained elusive even after decades of effort; but weak TCC can be proved easily for 4-colorable graphs. We noticed that in spite of the interest in studying $chi(G)$ in terms of $chi(G)$ right from the initial days, weak TCC is not proven to be true for $k$-colorable graphs even for $k=5$. In the second half of the paper, we make a contribution to the literature on total coloring by proving that $chi(G)leqDelta(G)+3$ for every 5-colorable graph $G$.
Motivated by a hat guessing problem proposed by Iwasawa cite{Iwasawa10}, Butler and Graham cite{Butler11} made the following conjecture on the existence of certain way of marking the {em coordinate lines} in $[k]^n$: there exists a way to mark one po int on each {em coordinate line} in $[k]^n$, so that every point in $[k]^n$ is marked exactly $a$ or $b$ times as long as the parameters $(a,b,n,k)$ satisfies that there are non-negative integers $s$ and $t$ such that $s+t = k^n$ and $as+bt = nk^{n-1}$. In this paper we prove this conjecture for any prime number $k$. Moreover, we prove the conjecture for the case when $a=0$ for general $k$.
We prove a conjecture of Ohba which says that every graph $G$ on at most $2chi(G)+1$ vertices satisfies $chi_ell(G)=chi(G)$.
We consider three graphs, $G_{7,3}$, $G_{7,4}$, and $G_{7,6}$, related to Kellers conjecture in dimension 7. The conjecture is false for this dimension if and only if at least one of the graphs contains a clique of size $2^7 = 128$. We present an aut omated method to solve this conjecture by encoding the existence of such a clique as a propositional formula. We apply satisfiability solving combined with symmetry-breaking techniques to determine that no such clique exists. This result implies that every unit cube tiling of $mathbb{R}^7$ contains a facesharing pair of cubes. Since a faceshare-free unit cube tiling of $mathbb{R}^8$ exists (which we also verify), this completely resolves Kellers conjecture.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا