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Regular graphs of high degree are 1factorizable
 PROC. LONDON MATH. SOC
, 1985
"... It is a wellknown conjecture that if a regular graph G of order 2n has degree d(G) satisfying d(G) ^ n, then G is the union of edgedisjoint 1factors. It is well known that this conjecture is true for d(G) equal to 2n —1 or 2n — 2. We show here that it is true for d(G) equal to2n — 3, In — 4, or2 ..."
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Cited by 14 (4 self)
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It is a wellknown conjecture that if a regular graph G of order 2n has degree d(G) satisfying d(G) ^ n, then G is the union of edgedisjoint 1factors. It is well known that this conjecture is true for d(G) equal to 2n —1 or 2n — 2. We show here that it is true for d(G) equal to2n — 3, In — 4, or2n — 5. We also show that it is true for </(G)>$K(G).
Chromatic Index Critical Graphs of Orders 11 and 12
, 1997
"... A chromaticindexcritical graph G on n vertices is nontrivial if it has at most \Deltab n 2 c edges. We prove that there is no chromaticindexcritical graph of order 12, and that there are precisely two nontrivial chromatic index critical graphs on 11 vertices. Together with known results thi ..."
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Cited by 3 (1 self)
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A chromaticindexcritical graph G on n vertices is nontrivial if it has at most \Deltab n 2 c edges. We prove that there is no chromaticindexcritical graph of order 12, and that there are precisely two nontrivial chromatic index critical graphs on 11 vertices. Together with known results this implies that there are precisely three nontrivial chromaticindex critical graphs of order 12. 1 Introduction A famous theorem of Vizing [20] states that the chromatic index Ø 0 (G) of a simple graph G is \Delta(G) or \Delta(G) + 1, where \Delta(G) denotes the maximum vertex degree in G. A graph G is class 1 if Ø 0 (G) = \Delta(G) and it is class 2 otherwise. A class 2 graph G is (chromatic index) critical if Ø 0 (G \Gamma e) ! Ø 0 (G) for each edge e of G. If we want to stress the maximum vertex degree of a critical graph G we say G is \Delta(G)critical. Critical graphs of odd order are easy to construct while not much is known about critical graphs of even order. One reas...
ChromaticIndex Critical Graphs of Even Order
, 1997
"... A kcritrical graph G has maximum degree k 0, chromatic index Ø 0 (G) = k + 1 and Ø 0 (G \Gamma e) ! k + 1 for each edge e of G. The Critical Graph Conjecture, Jakobsen [8] and Beineke, Wilson [1], claims that every kcritical graph is of odd order. Fiorini and Wilson [6] conjectured that ev ..."
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A kcritrical graph G has maximum degree k 0, chromatic index Ø 0 (G) = k + 1 and Ø 0 (G \Gamma e) ! k + 1 for each edge e of G. The Critical Graph Conjecture, Jakobsen [8] and Beineke, Wilson [1], claims that every kcritical graph is of odd order. Fiorini and Wilson [6] conjectured that every kcritical graph of even order has a 1factor. Chetwynd and Yap [4] stated the problem whether it is true that if G is a kcritical graph of odd order, then G \Gamma v has a 1factor for every vertex v of minimum degree. These conjectures are disproved and the problem is answered in the negative for k 2 f3; 4g. We disprove these conjectures and answer the problem in the negative for all k 3. We also construct kcritical graphs on n vertices with degree sequence 23 2 4 n\Gamma3 , answering a question of Yap [11]. 1 Introduction We consider connected multigraphs M = (V (M); E(M)) without loops, where V (M) (E(M)) denotes the set of vertices (edges) of M . The degree dM (v) of a v...
Theorems and Computations . . .
, 2007
"... The circular chromatic number provides a more refined measure of colourability of graphs, than does the ordinary chromatic number. Thus circular colouring is of substantial importance wherever graph colouring is studied or applied, for example, to scheduling problems of periodic nature. Precisely, ..."
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The circular chromatic number provides a more refined measure of colourability of graphs, than does the ordinary chromatic number. Thus circular colouring is of substantial importance wherever graph colouring is studied or applied, for example, to scheduling problems of periodic nature. Precisely, the circular chromatic number of a graph G, denoted by χc(G), is the smallest ratio p/q of positive integers p and q for which there exists a mapping c: V (G) → {1,2,...,p} such that q � c(u) − c(v)  � p − q for every edge uv of G. We present some known and new results regarding the computation of the circular chromatic number. In particular, we prove a lemma which can be used to improve the ratio of some circular colourings. These results are later used to bound the circular chromatic number of the plane unitdistance graph, the projective plane orthogonality graph, generalized Petersen graphs, and squares of graphs. Some of the computations in this thesis are computer assisted. Neˇsetˇril’s “pentagon problem”, asks whether the circular chromatic number of every cubic graph having sufficiently high girth is at most 5/2. We prove that the statement of the
Gunnar Brinkmann
, 2003
"... A graph is chromaticindexcritical if it cannot be edgecoloured with ∆ colours (with ∆ the maximal degree of the graph), and if the removal of any edge decreases its chromatic index. The Critical Graph Conjecture stated that any such graph has odd order. It has been proved false and the smallest k ..."
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A graph is chromaticindexcritical if it cannot be edgecoloured with ∆ colours (with ∆ the maximal degree of the graph), and if the removal of any edge decreases its chromatic index. The Critical Graph Conjecture stated that any such graph has odd order. It has been proved false and the smallest known counterexample has order 18 [18, 31]. In this paper we show that there are no chromaticindexcritical graphs of order 14. Our result extends that of [5] and leaves order 16 as the only case to be checked in order to decide on the minimality of the counterexample given by Chetwynd and Fiol. In addition we list all nontrivial critical graphs of order 13. Key words: critical graph, edgecolouring, graph generation. Math. Subj. Class (2001): 05C15, 05C30