On subgraphs of large girth
|
|
- Noreen McDonald
- 5 years ago
- Views:
Transcription
1 1/34 On subgraphs of large girth In Honor of the 50th Birthday of Thomas Vojtěch Rödl joint work with Domingos Dellamonica May, 2012
2 2/34
3 3/34
4 4/34
5 5/34
6 6/34
7 7/34 ARRANGEABILITY AND CLIQUE SUBDIVISIONS Vojtěch Rödl* Department of ematics and Computer Science Emory University Atlanta, GA and Thomas** School of ematics Georgia Institute of Technology Atlanta, GA ABSTRACT Let k be an integer. A graph G is k-arrangeable (concept introduced by Chen and Schelp) if the vertices of G can be numbered v1, v2,..., vn in such a way that for every integer i with 1 i n, at most k vertices among {v1, v2,..., vi} have a neighbor v {vi+1, vi+2,..., vn} that is adjacent to vi. We prove that for every integer p 1, if a graph G is not p 8 - arrangeable, then it contains a Kp-subdivision. By a result of Chen and Schelp this implies that graphs with no Kp-subdivision have linearly bounded Ramsey numbers, and by a result of Kierstead and Trotter it implies that such graphs have bounded game chromatic number.
8 8/34 An old question of Erdős and Hajnal Is it true that for every k and g there exists χ = χ(k, g) such that any graph G with χ(g) χ contains a subgraph H G with χ(h) k and girth(h) g?
9 8/34 An old question of Erdős and Hajnal Is it true that for every k and g there exists χ = χ(k, g) such that any graph G with χ(g) χ contains a subgraph H G with χ(h) k and girth(h) g? R (1977): True for g = 4, i.e., triangle-free subgraph H with large χ(h).
10 9/34 Thomassen s conjecture Let d(g) = 2e(G) v(g) denote the average degree of G. Conjecture (1983) For every k and g there exists D = D(k, g) such that any graph G with d(g) D contains a subgraph H G with d(h) k and girth(h) g.
11 9/34 Thomassen s conjecture Let d(g) = 2e(G) v(g) denote the average degree of G. Conjecture (1983) For every k and g there exists D = D(k, g) such that any graph G with d(g) D contains a subgraph H G with d(h) k and girth(h) g. Note: trivial to get rid of odd cycles by taking a bipartite subgraph H.
12 10/34 Known results Pyber, R, and Szemerédi (1995): true for all graphs G satisfying (G) e α k,g d(g).
13 10/34 Known results Pyber, R, and Szemerédi (1995): true for all graphs G satisfying (G) e α k,g d(g). Kühn and Osthus (2004): true for g 6, i.e., can obtain bipartite subgraph H which is C 4 -free;
14 10/34 Known results Pyber, R, and Szemerédi (1995): true for all graphs G satisfying (G) e α k,g d(g). Kühn and Osthus (2004): true for g 6, i.e., can obtain bipartite subgraph H which is C 4 -free; Dellamonica, Koubek, Martin, R. (2011): an alternative proof of the above result (next slides).
15 10/34 Known results Pyber, R, and Szemerédi (1995): true for all graphs G satisfying (G) e α k,g d(g). Kühn and Osthus (2004): true for g 6, i.e., can obtain bipartite subgraph H which is C 4 -free; Dellamonica, Koubek, Martin, R. (2011): an alternative proof of the above result (next slides). Dellamonica, R. (2011): true for all C 4 -free graphs G satisfying (G) e eβ k,g d(g) (this talk).
16 10/34 Known results Pyber, R, and Szemerédi (1995): true for all graphs G satisfying (G) e α k,g d(g). Kühn and Osthus (2004): true for g 6, i.e., can obtain bipartite subgraph H which is C 4 -free; Dellamonica, Koubek, Martin, R. (2011): an alternative proof of the above result (next slides). Dellamonica, R. (2011): true for all C 4 -free graphs G satisfying (G) e eβ k,g d(g) (this talk).
17 11/34 Alternative proof for g 6 Definition (Intersection Pattern) For k-partite k-graph H on V = V 1 V k, the intersection pattern of distinct e, f H is {i [k] : e V i = f V i }. Let P(H) denote the set of intersection patterns of all e f H. J = {2, 3} is an intersection pattern {
18 11/34 Alternative proof for g 6 Definition (Intersection Pattern) For k-partite k-graph H on V = V 1 V k, the intersection pattern of distinct e, f H is {i [k] : e V i = f V i }. Let P(H) denote the set of intersection patterns of all e f H. Definition (Star, Kernel) A hypergraph S is a star with kernel K if for all distinct e, f S, e f = K.
19 12/34 Alternative proof for g 6 Definition (Strong) A k-partite k-graph H is called t-strong if for every J P(H ) and e H there is a star S H, containing e, with kernel e J and S = t.
20 12/34 Alternative proof for g 6 Definition (Strong) A k-partite k-graph H is called t-strong if for every J P(H ) and e H there is a star S H, containing e, with kernel e J and S = t. J = {2, 3} is an intersection pattern {
21 12/34 Alternative proof for g 6 Definition (Strong) A k-partite k-graph H is called t-strong if for every J P(H ) and e H there is a star S H, containing e, with kernel e J and S = t. e J = {v 2, v 3 } {
22 12/34 Alternative proof for g 6 Definition (Strong) A k-partite k-graph H is called t-strong if for every J P(H ) and e H there is a star S H, containing e, with kernel e J and S = t. A t-star for t = 3 {
23 13/34 Alternative proof for g 6 Lemma (Füredi, 1983) For every k, t, there exists c = c(k, t) such that any k-graph H contains a t-strong subhypergraph H with H c H.
24 14/34 A common trick: take a bipartite subgraph From arbitrary G 0 with d(g 0 ) D k, get G G 0 with δ = δ(g) d(g 0 )/2.
25 14/34 A common trick: take a bipartite subgraph From arbitrary G 0 with d(g 0 ) D k, get G G 0 with δ = δ(g) d(g 0 )/2.
26 14/34 A common trick: take a bipartite subgraph From arbitrary G 0 with d(g 0 ) D k, get G G 0 with δ = δ(g) d(g 0 )/2.
27 14/34 A common trick: take a bipartite subgraph From arbitrary G 0 with d(g 0 ) D k, get G G 0 with δ = δ(g) d(g 0 )/2.
28 15/34 A common trick: take a bipartite subgraph Repeat until no more edge between vertices of degree > δ.
29 15/34 A common trick: take a bipartite subgraph First case: at least half of the edges are red = G red is almost regular, i.e. (G red ) δ = O(d(G red )).
30 15/34 A common trick: take a bipartite subgraph First case: at least half of the edges are red = G red is almost regular, i.e. (G red ) δ = O(d(G red )). Pyber-R-Szemerédi: G red contains subgraph H with d(h) k and girth(h) g.
31 15/34 A common trick: take a bipartite subgraph Second case: at least half of the edges are purple (crossing). Then set A = red set, B = blue set and G = (A, B; E) = G purple.
32 16/34 Applying Füredi s Lemma A little more work yields a bipartite graph G = (A, B; E) where deg G (v) = d k for all v A and, N G (v) N G (w) for all v w A.
33 16/34 Applying Füredi s Lemma A little more work yields a bipartite graph G = (A, B; E) where deg G (v) = d k for all v A and, N G (v) N G (w) for all v w A. Define H as a d-graph with V (H) = B and edge set { NG (v) : v A }.
34 16/34 Applying Füredi s Lemma A little more work yields a bipartite graph G = (A, B; E) where deg G (v) = d k for all v A and, N G (v) N G (w) for all v w A. Define H as a d-graph with V (H) = B and edge set { NG (v) : v A }. Apply Füredi s Lemma with some large t: H H is d-partite and t-strong. Note H A A.
35 17/34 The hypergraph from Füredi s Lemma
36 18/34 Dichotomy Recall P(H ) 2 [d] is the family of all intersection patterns of H. Let Γ be the shadow graph of P(H ): ( Γ = [d], { {i, j} : J P(H ), J {i, j} }).
37 18/34 Dichotomy Recall P(H ) 2 [d] is the family of all intersection patterns of H. Let Γ be the shadow graph of P(H ): ( Γ = [d], { {i, j} : J P(H ), J {i, j} }). Either 1 Γ has a large independent set I, or
38 18/34 Dichotomy Recall P(H ) 2 [d] is the family of all intersection patterns of H. Let Γ be the shadow graph of P(H ): ( Γ = [d], { {i, j} : J P(H ), J {i, j} }). Either 1 Γ has a large independent set I, or 2 (Γ), the max degree of Γ, is large.
39 19/34 Alternative Proof for g = 6 1 Γ has a large independent set I = the desired subgraph H (d(h) I k and girth(h) 6).
40 19/34 Alternative Proof for g = 6 1 Γ has a large independent set I = the desired subgraph H (d(h) I k and girth(h) 6). Claim. If B = B 1 B d are the classes of H, then H = G [ A, i I B i] is C4 -free.
41 19/34 Alternative Proof for g = 6 1 Γ has a large independent set I = the desired subgraph H (d(h) I k and girth(h) 6). Claim. If B = B 1 B d are the classes of H, then H = G [ A, i I B i] is C4 -free. Proof. If not...
42 19/34 Alternative Proof for g = 6 1 Γ has a large independent set I = the desired subgraph H (d(h) I k and girth(h) 6). Claim. If B = B 1 B d are the classes of H, then H = G [ A, i I B i] is C4 -free. Proof. If not...
43 19/34 Alternative Proof for g = 6 1 Γ has a large independent set I = the desired subgraph H (d(h) I k and girth(h) 6). Claim. If B = B 1 B d are the classes of H, then H = G [ A, i I B i] is C4 -free. Proof. If not... The intersection pattern J of e 1 e 2 contains {i 2, i 4 } I. Hence {i 2, i 4 } Γ, a contradiction!
44 20/34 Alternative Proof for g = 6 2 (Γ) is large = vertex b B, X b N G (b), Y b B \ {b} such that G[X b, Y b ] has large degrees.
45 20/34 Alternative Proof for g = 6 2 (Γ) is large = vertex b B, X b N G (b), Y b B \ {b} such that G[X b, Y b ] has large degrees. Proof of 2 :
46 20/34 Alternative Proof for g = 6 2 (Γ) is large = vertex b B, X b N G (b), Y b B \ {b} such that G[X b, Y b ] has large degrees. Proof of 2 :
47 20/34 Alternative Proof for g = 6 2 (Γ) is large = vertex b B, X b N G (b), Y b B \ {b} such that G[X b, Y b ] has large degrees. Proof of 2 :
48 20/34 Alternative Proof for g = 6 2 (Γ) is large = vertex b B, X b N G (b), Y b B \ {b} such that G[X b, Y b ] has large degrees. Proof of 2 :
49 20/34 Alternative Proof for g = 6 2 (Γ) is large = vertex b B, X b N G (b), Y b B \ {b} such that G[X b, Y b ] has large degrees. Proof of 2 :
50 20/34 Alternative Proof for g = 6 2 (Γ) is large = vertex b B, X b N G (b), Y b B \ {b} such that G[X b, Y b ] has large degrees. Proof of 2 :
51 20/34 Alternative Proof for g = 6 2 (Γ) is large = vertex b B, X b N G (b), Y b B \ {b} such that G[X b, Y b ] has large degrees. Proof of 2 :
52 21/34 Alternative Proof for g = 6 Proof of Theorem. If 1 holds for G, we are done! Otherwise 2 holds...
53 21/34 Alternative Proof for g = 6 Proof of Theorem. If 1 holds for G, we are done! Otherwise 2 holds...
54 21/34 Alternative Proof for g = 6 Proof of Theorem. If 1 holds for G[X b0, Y b0 ], we are done! Otherwise 2 holds...
55 21/34 Alternative Proof for g = 6 Proof of Theorem. If 1 holds for G[X b0, Y b0 ], we are done! Otherwise 2 holds...
56 21/34 Alternative Proof for g = 6 Proof of Theorem. If 1 holds for G[X b1, Y b1 ], we are done! Otherwise 2 holds...
57 21/34 Alternative Proof for g = 6 Proof of Theorem.
58 21/34 Alternative Proof for g = 6 Proof of Theorem. Found a complete bipartite subgraph G[{b 0,..., b m }, X bm ].
59 22/34 Question Is there a hypergraph lemma similar to Füredi s that could be used to prove the general case of the conjecture? More modestly, is there a hypergraph lemma that would allow us to prove the g = 8 case?
60 23/34 Lemma (Dellamonica R, 2011) For all k and g there exist c and d 0 such that the following holds. In any C 4 -free bipartite graph G = (A, B; E) satisfying d max { c log log (G), d 0 }, there exists H G such that d(h) k and girth(h) g.
61 24/34 Using the result of Kühn Osthus (the numerical bounds in DKMR are inferior), yields: Theorem For all k and g there exist α, β, and d 0 such that for any graph G with d(g) max { α ( log log (G) ) β, d0 } there exists H G such that d(h) k and girth(h) g.
62 24/34 Using the result of Kühn Osthus (the numerical bounds in DKMR are inferior), yields: Theorem For all k and g there exist α, β, and d 0 such that for any graph G with d(g) max { α ( log log (G) ) β, d0 } there exists H G such that d(h) k and girth(h) g. Recall: Pyber-R-Szemerédi yields same conclusion under stronger assumption d c log (G).
63 25/34 Proof of our lemma Assume wlog that G = (A, B; E) is such deg G (v) = d for all v A and B A. Take ϱ = e α k,g d, ε > 0, and partition B = B 0 B 1 B t, where B 0 = { v B : deg G (v) ϱ }, and B j = { v B : ϱ (1+ε)j 1 < deg G (v) ϱ (1+ε)j }, for j = 1,..., t.
64 25/34 Proof of our lemma Assume wlog that G = (A, B; E) is such deg G (v) = d for all v A and B A. Take ϱ = e α k,g d, ε > 0, and partition B = B 0 B 1 B t, where B 0 = { v B : deg G (v) ϱ }, and B j = { v B : ϱ (1+ε)j 1 < deg G (v) ϱ (1+ε)j }, for j = 1,..., t. t = O ( log log (G) ). For appropriate choice of c = c(k, g), (G) e ecd = t < d 8k.
65 26/34 Proof of our lemma
66 26/34 Proof of our lemma Easy case: e G (A, B 0 ) e(g) 2. Take G = G[A B 0 ] and note that (G ) ϱ e c d(g ). Pyber R Szemerédi s result implies that G contains the graph we are looking for.
67 27/34 Proof of our lemma Otherwise: by averaging, there exists j [t] such that t i=1 e G (A, B j ) e G (A, B i ) t e(g) d A 2t 2 d 8k = e(g) e G (A, B 0 ) t = 4k A.
68 27/34 Proof of our lemma Otherwise: by averaging, there exists j [t] such that { } e G (A, B j ) max 4k A, ϱ (1+ε)j 1 B j.
69 27/34 Proof of our lemma Otherwise: by averaging, there exists j [t] such that { } e G (A, B j ) max 4k A, ϱ (1+ε)j 1 B j. 1 Delete all vertices in B \ B j. 2 Sequentially delete vertices from A with degree < k and vertices of B j with degree < D/4, where D = ϱ (1+ε)j 1.
70 27/34 Proof of our lemma Otherwise: by averaging, there exists j [t] such that { } e G (A, B j ) max 4k A, ϱ (1+ε)j 1 B j. 1 Delete all vertices in B \ B j. 2 Sequentially delete vertices from A with degree < k and vertices of B j with degree < D/4, where D = ϱ (1+ε)j 1. Note: deleted at most k A + D 4 B j < e G (A, B j ) 2 edges.
71 28/34 Proof of our lemma Result: non-empty graph G with classes A and B = B j such that degrees in A are between k and d; degrees in B are between D/4 and D (1+ε) = ϱ (1+ε)j.
72 29/34 Back to hypergraphs Let H be a hypergraph with vertex set B and edges { NG (v) : v A }. Obs. 1: G is C 4 -free = e f 1 for all e, f H (i.e., H is a linear hypergraph).
73 29/34 Back to hypergraphs Let H be a hypergraph with vertex set B and edges { NG (v) : v A }. Obs. 1: G is C 4 -free = e f 1 for all e, f H (i.e., H is a linear hypergraph). Obs. 2: a cycle of length 2l in G corresponds to a cycle of length l in H: i.e., cycle (v 0, v 1,..., v 2l 1 ) corresponds to (e 0, e 1,..., e l 1 ), where e i = N G (v 2i ) H.
74 30/34 Cycles in linear hypergraphs Recall: δ(h) D/4 and (H) D 1+ε. Let s count cycles of length l.
75 30/34 Cycles in linear hypergraphs Recall: δ(h) D/4 and (H) D 1+ε. Let s count cycles of length l. 1 Pick an edge e 0 H... # H
76 30/34 Cycles in linear hypergraphs Recall: δ(h) D/4 and (H) D 1+ε. Let s count cycles of length l. 1 Pick an edge e 0 H... 2 and w 0 w 1 e 0... # H d 2
77 30/34 Cycles in linear hypergraphs Recall: δ(h) D/4 and (H) D 1+ε. Let s count cycles of length l. 1 Pick an edge e 0 H... 2 and w 0 w 1 e and e 1 w 1... # H d 2 D 1+ε
78 30/34 Cycles in linear hypergraphs Recall: δ(h) D/4 and (H) D 1+ε. Let s count cycles of length l. 1 Pick an edge e 0 H... 2 and w 0 w 1 e and e 1 w and w 2 e 1... # H d 2 D 1+ε d
79 30/34 Cycles in linear hypergraphs Recall: δ(h) D/4 and (H) D 1+ε. Let s count cycles of length l. 1 Pick an edge e 0 H... 2 and w 0 w 1 e and e 1 w and w 2 e # H d 2 D 1+ε d
80 30/34 Cycles in linear hypergraphs Recall: δ(h) D/4 and (H) D 1+ε. Let s count cycles of length l. 1 Pick an edge e 0 H... 2 and w 0 w 1 e and e 1 w and w 2 e and w l 1 e l 2... # H d l D (1+ε)(l 2)
81 30/34 Cycles in linear hypergraphs Recall: δ(h) D/4 and (H) D 1+ε. Let s count cycles of length l. 1 Pick an edge e 0 H... 2 and w 0 w 1 e and e 1 w and w 2 e and w l 1 e l at most one possible edge e l 1 v 0, v 2l 1. # H d l D (1+ε)(l 2) 1.
82 31/34 Cycles in linear hypergraphs Result: Number of cycles of length l is N l H d l D (1+ε)(l 2).
83 31/34 Cycles in linear hypergraphs Result: Number of cycles of length l is N l H d l D (1+ε)(l 2). Randomly select edges of H with probability p. How many cycles survive? In expectation, at most p l N l (p H ) p l 1 d l D (1+ε)(l 2).
84 31/34 Cycles in linear hypergraphs Result: Number of cycles of length l is N l H d l D (1+ε)(l 2). Randomly select edges of H with probability p. How many cycles survive? In expectation, at most p l N l (p H ) p l 1 d l D (1+ε)(l 2). }{{} 1 for small p
85 31/34 Cycles in linear hypergraphs Result: Number of cycles of length l is N l H d l D (1+ε)(l 2). Randomly select edges of H with probability p. How many cycles survive? In expectation, at most p l N l (p H ) p l 1 d l D (1+ε)(l 2). }{{} 1 for small p Linearity of expectation: p = D ε 1, ε = 1 2g = # of surviving edges is much larger than # of surviving cycles of length l < g/2.
86 31/34 Cycles in linear hypergraphs Result: Number of cycles of length l is N l H d l D (1+ε)(l 2). Randomly select edges of H with probability p. How many cycles survive? In expectation, at most p l N l (p H ) p l 1 d l D (1+ε)(l 2). }{{} 1 for small p Linearity of expectation: p = D ε 1, ε = 1 2g = # of surviving edges is much larger than # of surviving cycles of length l < g/2. Delete an edge for each cycle and destroy them all! Resulting hypergraph H has Ω ( D ε V (H) ) edges and no cycles of length < g/2.
87 32/34 Back to graphs Recall: edges of H correspond to vertices in A A (e H v A, e = N G (v)).
88 32/34 Back to graphs Recall: edges of H correspond to vertices in A A (e H v A, e = N G (v)). Let H be the induced subgraph G [ A V (H ) ]. girth(h) g because girth(h ) g/2;
89 32/34 Back to graphs Recall: edges of H correspond to vertices in A A (e H v A, e = N G (v)). Let H be the induced subgraph G [ A V (H ) ]. girth(h) g because girth(h ) g/2; by construction, deg H (v) k for all v A, thus d(h) = 2e(H) v(h) 2k A A + V (H ) = 2k H H + V (H ) > k.
90 32/34 Back to graphs Recall: edges of H correspond to vertices in A A (e H v A, e = N G (v)). Let H be the induced subgraph G [ A V (H ) ]. girth(h) g because girth(h ) g/2; by construction, deg H (v) k for all v A, thus d(h) = 2e(H) v(h) 2k A A + V (H ) = 2k H H + V (H ) > k.
91 32/34 Back to graphs Recall: edges of H correspond to vertices in A A (e H v A, e = N G (v)). Let H be the induced subgraph G [ A V (H ) ]. girth(h) g because girth(h ) g/2; by construction, deg H (v) k for all v A, thus d(h) = 2e(H) v(h) 2k A A + V (H ) = 2k H H + V (H ) > k. Hence, H is the desired subgraph!
92 33/34 Open questions The conjectures of Thomassen and Erdős Hajnal remain open. Is there a hypergraph lemma similar to Füredi s that can be used to prove Thomassen s conjecture for, say, g = 8? Can one extend the gap between d(g) and (G) for which we can establish that the conjecture is true? Hypergraph version of Thomassen s conjecture: any degree-gap result in hypergraphs extends to graphs from our proof. Here the degree gap is polynomial (H) δ(h) 1+ε.
93 34/34
ARRANGEABILITY AND CLIQUE SUBDIVISIONS. Department of Mathematics and Computer Science Emory University Atlanta, GA and
ARRANGEABILITY AND CLIQUE SUBDIVISIONS Vojtěch Rödl* Department of Mathematics and Computer Science Emory University Atlanta, GA 30322 and Robin Thomas** School of Mathematics Georgia Institute of Technology
More informationINDUCED CYCLES AND CHROMATIC NUMBER
INDUCED CYCLES AND CHROMATIC NUMBER A.D. SCOTT DEPARTMENT OF MATHEMATICS UNIVERSITY COLLEGE, GOWER STREET, LONDON WC1E 6BT Abstract. We prove that, for any pair of integers k, l 1, there exists an integer
More informationPaul Erdős and Graph Ramsey Theory
Paul Erdős and Graph Ramsey Theory Benny Sudakov ETH and UCLA Ramsey theorem Ramsey theorem Definition: The Ramsey number r(s, n) is the minimum N such that every red-blue coloring of the edges of a complete
More informationOn the chromatic number and independence number of hypergraph products
On the chromatic number and independence number of hypergraph products Dhruv Mubayi Vojtĕch Rödl January 10, 2004 Abstract The hypergraph product G H has vertex set V (G) V (H), and edge set {e f : e E(G),
More informationThe regularity method and blow-up lemmas for sparse graphs
The regularity method and blow-up lemmas for sparse graphs Y. Kohayakawa (São Paulo) SPSAS Algorithms, Combinatorics and Optimization University of São Paulo July 2016 Partially supported CAPES/DAAD (430/15),
More informationChromatic number, clique subdivisions, and the conjectures of Hajós and Erdős-Fajtlowicz
Chromatic number, clique subdivisions, and the conjectures of Hajós and Erdős-Fajtlowicz Jacob Fox Choongbum Lee Benny Sudakov Abstract For a graph G, let χ(g) denote its chromatic number and σ(g) denote
More informationBipartite Graph Tiling
Bipartite Graph Tiling Yi Zhao Department of Mathematics and Statistics Georgia State University Atlanta, GA 30303 December 4, 008 Abstract For each s, there exists m 0 such that the following holds for
More informationOn the Regularity Method
On the Regularity Method Gábor N. Sárközy 1 Worcester Polytechnic Institute USA 2 Computer and Automation Research Institute of the Hungarian Academy of Sciences Budapest, Hungary Co-authors: P. Dorbec,
More informationarxiv: v1 [math.co] 2 Dec 2013
What is Ramsey-equivalent to a clique? Jacob Fox Andrey Grinshpun Anita Liebenau Yury Person Tibor Szabó arxiv:1312.0299v1 [math.co] 2 Dec 2013 November 4, 2018 Abstract A graph G is Ramsey for H if every
More informationJacques Verstraëte
2 - Turán s Theorem Jacques Verstraëte jacques@ucsd.edu 1 Introduction The aim of this section is to state and prove Turán s Theorem [17] and to discuss some of its generalizations, including the Erdős-Stone
More informationOn (δ, χ)-bounded families of graphs
On (δ, χ)-bounded families of graphs András Gyárfás Computer and Automation Research Institute Hungarian Academy of Sciences Budapest, P.O. Box 63 Budapest, Hungary, H-1518 gyarfas@sztaki.hu Manouchehr
More informationLarge topological cliques in graphs without a 4-cycle
Large topological cliques in graphs without a 4-cycle Daniela Kühn Deryk Osthus Abstract Mader asked whether every C 4 -free graph G contains a subdivision of a complete graph whose order is at least linear
More informationTiling on multipartite graphs
Tiling on multipartite graphs Ryan Martin Mathematics Department Iowa State University rymartin@iastate.edu SIAM Minisymposium on Graph Theory Joint Mathematics Meetings San Francisco, CA Ryan Martin (Iowa
More informationC-Perfect K-Uniform Hypergraphs
C-Perfect K-Uniform Hypergraphs Changiz Eslahchi and Arash Rafiey Department of Mathematics Shahid Beheshty University Tehran, Iran ch-eslahchi@cc.sbu.ac.ir rafiey-ar@ipm.ir Abstract In this paper we define
More informationThe regularity method and blow-up lemmas for sparse graphs
The regularity method and blow-up lemmas for sparse graphs Y. Kohayakawa (São Paulo) SPSAS Algorithms, Combinatorics and Optimization University of São Paulo July 2016 Partially supported CAPES/DAAD (430/15),
More informationCycles with consecutive odd lengths
Cycles with consecutive odd lengths arxiv:1410.0430v1 [math.co] 2 Oct 2014 Jie Ma Department of Mathematical Sciences, Carnegie Mellon University, Pittsburgh, PA 15213. Abstract It is proved that there
More informationVERTEX DEGREE SUMS FOR PERFECT MATCHINGS IN 3-UNIFORM HYPERGRAPHS
VERTEX DEGREE SUMS FOR PERFECT MATCHINGS IN 3-UNIFORM HYPERGRAPHS YI ZHANG, YI ZHAO, AND MEI LU Abstract. We determine the minimum degree sum of two adjacent vertices that ensures a perfect matching in
More informationOn the size-ramsey numbers for hypergraphs. A. Dudek, S. La Fleur and D. Mubayi
On the size-ramsey numbers for hypergraphs A. Dudek, S. La Fleur and D. Mubayi REPORT No. 48, 013/014, spring ISSN 1103-467X ISRN IML-R- -48-13/14- -SE+spring On the size-ramsey number of hypergraphs Andrzej
More informationEquitable coloring of random graphs
Michael Krivelevich 1, Balázs Patkós 2 1 Tel Aviv University, Tel Aviv, Israel 2 Central European University, Budapest, Hungary Phenomena in High Dimensions, Samos 2007 A set of vertices U V (G) is said
More informationPartitioning 2-edge-colored Ore-type graphs by monochromatic cycles
Partitioning 2-edge-colored Ore-type graphs by monochromatic cycles János Barát MTA-ELTE Geometric and Algebraic Combinatorics Research Group barat@cs.elte.hu and Gábor N. Sárközy Alfréd Rényi Institute
More information1. Introduction Given k 2, a k-uniform hypergraph (in short, k-graph) consists of a vertex set V and an edge set E ( V
MINIMUM VERTEX DEGREE THRESHOLD FOR C 4-TILING JIE HAN AND YI ZHAO Abstract. We prove that the vertex degree threshold for tiling C4 (the - uniform hypergraph with four vertices and two triples in a -uniform
More informationAn asymptotic multipartite Kühn-Osthus theorem
An asymptotic multipartite Kühn-Osthus theorem Ryan R. Martin 1 Richard Mycroft 2 Jozef Skokan 3 1 Iowa State University 2 University of Birmingham 3 London School of Economics 08 August 2017 Algebraic
More informationPerfect divisibility and 2-divisibility
Perfect divisibility and 2-divisibility Maria Chudnovsky Princeton University, Princeton, NJ 08544, USA Vaidy Sivaraman Binghamton University, Binghamton, NY 13902, USA April 20, 2017 Abstract A graph
More informationGRAPH EMBEDDING LECTURE NOTE
GRAPH EMBEDDING LECTURE NOTE JAEHOON KIM Abstract. In this lecture, we aim to learn several techniques to find sufficient conditions on a dense graph G to contain a sparse graph H as a subgraph. In particular,
More informationThe typical structure of graphs without given excluded subgraphs + related results
The typical structure of graphs without given excluded subgraphs + related results Noga Alon József Balogh Béla Bollobás Jane Butterfield Robert Morris Dhruv Mubayi Wojciech Samotij Miklós Simonovits.
More informationR(p, k) = the near regular complete k-partite graph of order p. Let p = sk+r, where s and r are positive integers such that 0 r < k.
MATH3301 EXTREMAL GRAPH THEORY Definition: A near regular complete multipartite graph is a complete multipartite graph with orders of its partite sets differing by at most 1. R(p, k) = the near regular
More informationDegree Ramsey numbers for even cycles
Degree Ramsey numbers for even cycles Michael Tait Abstract Let H s G denote that any s-coloring of E(H) contains a monochromatic G. The degree Ramsey number of a graph G, denoted by R (G, s), is min{
More informationSubdivisions of a large clique in C 6 -free graphs
Subdivisions of a large clique in C 6 -free graphs József Balogh Hong Liu Maryam Sharifzadeh October 8, 2014 Abstract Mader conjectured that every C 4 -free graph has a subdivision of a clique of order
More informationRandom Graphs III. Y. Kohayakawa (São Paulo) Chorin, 4 August 2006
Y. Kohayakawa (São Paulo) Chorin, 4 August 2006 Outline 1 Outline of Lecture III 1. Subgraph containment with adversary: Existence of monoχ subgraphs in coloured random graphs; properties of the form G(n,
More informationProof of the (n/2 n/2 n/2) Conjecture for large n
Proof of the (n/2 n/2 n/2) Conjecture for large n Yi Zhao Department of Mathematics and Statistics Georgia State University Atlanta, GA 30303 September 9, 2009 Abstract A conjecture of Loebl, also known
More informationOn the bandwidth conjecture for 3-colourable graphs
On the bandwidth conjecture for 3-colourable graphs Julia Böttcher Technische Universität München Symposium on Discrete Algorithms, January 2007, New Orleans (joint work with Mathias Schacht & Anusch Taraz)
More informationFinite Induced Graph Ramsey Theory: On Partitions of Subgraphs
inite Induced Graph Ramsey Theory: On Partitions of Subgraphs David S. Gunderson and Vojtěch Rödl Emory University, Atlanta GA 30322. Norbert W. Sauer University of Calgary, Calgary, Alberta, Canada T2N
More informationOn tight cycles in hypergraphs
On tight cycles in hypergraphs Hao Huang Jie Ma Abstract A tight k-uniform l-cycle, denoted by T Cl k, is a k-uniform hypergraph whose vertex set is v 0,, v l 1, and the edges are all the k-tuples {v i,
More informationOn the Chromatic Thresholds of Hypergraphs
On the Chromatic Thresholds of Hypergraphs József Balogh Jane Butterfield Ping Hu John Lenz Dhruv Mubayi September 14, 2011 Abstract Let F be a family of r-uniform hypergraphs. The chromatic threshold
More informationOn colorability of graphs with forbidden minors along paths and circuits
On colorability of graphs with forbidden minors along paths and circuits Elad Horev horevel@cs.bgu.ac.il Department of Computer Science Ben-Gurion University of the Negev Beer-Sheva 84105, Israel Abstract.
More informationON EVEN-DEGREE SUBGRAPHS OF LINEAR HYPERGRAPHS
ON EVEN-DEGREE SUBGRAPHS OF LINEAR HYPERGRAPHS D. DELLAMONICA JR., P. HAXELL, T. LUCZAK, D. MUBAYI, B. NAGLE, Y. PERSON, V. RÖDL, M. SCHACHT, AND J. VERSTRAËTE Abstract. A subgraph of a hypergraph H is
More informationOn the Turán number of forests
On the Turán number of forests Bernard Lidický Hong Liu Cory Palmer April 13, 01 Abstract The Turán number of a graph H, ex(n, H, is the maximum number of edges in a graph on n vertices which does not
More informationON THE STRUCTURE OF ORIENTED GRAPHS AND DIGRAPHS WITH FORBIDDEN TOURNAMENTS OR CYCLES
ON THE STRUCTURE OF ORIENTED GRAPHS AND DIGRAPHS WITH FORBIDDEN TOURNAMENTS OR CYCLES DANIELA KÜHN, DERYK OSTHUS, TIMOTHY TOWNSEND, YI ZHAO Abstract. Motivated by his work on the classification of countable
More informationColoring Simple Hypergraphs
Department of Mathematics, Statistics and Computer Science University of Illinois Chicago May 13, 2011 A Puzzle Problem Let n 2 and suppose that S [n] [n] with S 2n 1. Then some three points in S determine
More informationInduced Cycles of Fixed Length
Induced Cycles of Fixed Length Terry McKee Wright State University Dayton, Ohio USA terry.mckee@wright.edu Cycles in Graphs Vanderbilt University 31 May 2012 Overview 1. Investigating the fine structure
More informationInduced subgraphs of graphs with large chromatic number. I. Odd holes
Induced subgraphs of graphs with large chromatic number. I. Odd holes Alex Scott Mathematical Institute, University of Oxford, Oxford OX2 6GG, UK Paul Seymour 1 Princeton University, Princeton, NJ 08544,
More informationOn Ramsey numbers of uniform hypergraphs with given maximum degree
Journal of Combinatorial Theory, Series A 113 (2006) 1555 1564 www.elsevier.com/locate/jcta ote On Ramsey numbers of uniform hypergraphs with given maximum degree A.V. Kostochka a,b,1, V. Rödl c,2 a Department
More informationMonochromatic tree covers and Ramsey numbers for set-coloured graphs
Monochromatic tree covers and Ramsey numbers for set-coloured graphs Sebastián Bustamante and Maya Stein Department of Mathematical Engineering University of Chile August 31, 2017 Abstract We consider
More informationGraph Minors Theory. Bahman Ghandchi. Institute for Advanced Studies in Basic Sciences (IASBS) SBU weekly Combinatorics Seminars November 5, 2011
Graph Minors Theory Bahman Ghandchi Institute for Advanced Studies in Basic Sciences (IASBS) SBU weekly Combinatorics Seminars November 5, 2011 Institute for Advanced Studies in asic Sciences Gava Zang,
More informationColoring Simple Hypergraphs
Department of Mathematics, Statistics and Computer Science University of Illinois Chicago August 28, 2010 Problem Let n 2 and suppose that S [n] [n] with S 2n 1. Then some three points in S determine a
More informationA NOTE ON THE TURÁN FUNCTION OF EVEN CYCLES
PROCEEDINGS OF THE AMERICAN MATHEMATICAL SOCIETY Volume 00, Number 0, Pages 000 000 S 0002-9939(XX)0000-0 A NOTE ON THE TURÁN FUNCTION OF EVEN CYCLES OLEG PIKHURKO Abstract. The Turán function ex(n, F
More informationChromatic Ramsey number of acyclic hypergraphs
Chromatic Ramsey number of acyclic hypergraphs András Gyárfás Alfréd Rényi Institute of Mathematics Hungarian Academy of Sciences Budapest, P.O. Box 127 Budapest, Hungary, H-1364 gyarfas@renyi.hu Alexander
More informationApplications of the Sparse Regularity Lemma
Applications of the Sparse Regularity Lemma Y. Kohayakawa (Emory and São Paulo) Extremal Combinatorics II DIMACS 2004 1 Szemerédi s regularity lemma 1. Works very well for large, dense graphs: n-vertex
More informationTurán numbers of expanded hypergraph forests
Turán numbers of expanded forests Rényi Institute of Mathematics, Budapest, Hungary Probabilistic and Extremal Combinatorics, IMA, Minneapolis, Sept. 9, 2014. Main results are joint with Tao JIANG, Miami
More informationPacking k-partite k-uniform hypergraphs
Available online at www.sciencedirect.com Electronic Notes in Discrete Mathematics 38 (2011) 663 668 www.elsevier.com/locate/endm Packing k-partite k-uniform hypergraphs Richard Mycroft 1 School of Mathematical
More informationAcyclic subgraphs with high chromatic number
Acyclic subgraphs with high chromatic number Safwat Nassar Raphael Yuster Abstract For an oriented graph G, let f(g) denote the maximum chromatic number of an acyclic subgraph of G. Let f(n) be the smallest
More informationTopics on Computing and Mathematical Sciences I Graph Theory (7) Coloring II
Topics on Computing and Mathematical Sciences I Graph Theory (7) Coloring II Yoshio Okamoto Tokyo Institute of Technology June 4, 2008 Plan changed 4/09 Definition of Graphs; Paths and Cycles 4/16 Cycles;
More informationOn the Chromatic Thresholds of Hypergraphs
On the Chromatic Thresholds of Hypergraphs József Balogh Jane Butterfield Ping Hu John Lenz Dhruv Mubayi October 5, 013 Abstract Let F be a family of r-uniform hypergraphs. The chromatic threshold of F
More informationAn approximate version of Hadwiger s conjecture for claw-free graphs
An approximate version of Hadwiger s conjecture for claw-free graphs Maria Chudnovsky Columbia University, New York, NY 10027, USA and Alexandra Ovetsky Fradkin Princeton University, Princeton, NJ 08544,
More informationarxiv: v1 [math.co] 23 Nov 2015
arxiv:1511.07306v1 [math.co] 23 Nov 2015 RAMSEY NUMBERS OF TREES AND UNICYCLIC GRAPHS VERSUS FANS MATTHEW BRENNAN Abstract. The generalized Ramsey number R(H, K) is the smallest positive integer n such
More informationColoring. Basics. A k-coloring of a loopless graph G is a function f : V (G) S where S = k (often S = [k]).
Coloring Basics A k-coloring of a loopless graph G is a function f : V (G) S where S = k (often S = [k]). For an i S, the set f 1 (i) is called a color class. A k-coloring is called proper if adjacent
More informationThe typical structure of sparse K r+1 -free graphs
The typical structure of sparse K r+1 -free graphs Lutz Warnke University of Cambridge (joint work with József Balogh, Robert Morris, and Wojciech Samotij) H-free graphs / Turán s theorem Definition Let
More informationEdge-disjoint induced subgraphs with given minimum degree
Edge-disjoint induced subgraphs with given minimum degree Raphael Yuster Department of Mathematics University of Haifa Haifa 31905, Israel raphy@math.haifa.ac.il Submitted: Nov 9, 01; Accepted: Feb 5,
More informationTopics on Computing and Mathematical Sciences I Graph Theory (6) Coloring I
Topics on Computing and Mathematical Sciences I Graph Theory (6) Coloring I Yoshio Okamoto Tokyo Institute of Technology May, 008 Last updated: Wed May 6: 008 Y. Okamoto (Tokyo Tech) TCMSI Graph Theory
More information9 - The Combinatorial Nullstellensatz
9 - The Combinatorial Nullstellensatz Jacques Verstraëte jacques@ucsd.edu Hilbert s nullstellensatz says that if F is an algebraically closed field and f and g 1, g 2,..., g m are polynomials in F[x 1,
More informationarxiv:math/ v1 [math.co] 17 Apr 2002
arxiv:math/0204222v1 [math.co] 17 Apr 2002 On Arithmetic Progressions of Cycle Lengths in Graphs Jacques Verstraëte Department of Pure Mathematics and Mathematical Statistics Centre for Mathematical Sciences
More informationInduced subgraphs of prescribed size
Induced subgraphs of prescribed size Noga Alon Michael Krivelevich Benny Sudakov Abstract A subgraph of a graph G is called trivial if it is either a clique or an independent set. Let q(g denote the maximum
More informationKatarzyna Mieczkowska
Katarzyna Mieczkowska Uniwersytet A. Mickiewicza w Poznaniu Erdős conjecture on matchings in hypergraphs Praca semestralna nr 1 (semestr letni 010/11 Opiekun pracy: Tomasz Łuczak ERDŐS CONJECTURE ON MATCHINGS
More informationGraph Packing - Conjectures and Results
Graph Packing p.1/23 Graph Packing - Conjectures and Results Hemanshu Kaul kaul@math.iit.edu www.math.iit.edu/ kaul. Illinois Institute of Technology Graph Packing p.2/23 Introduction Let G 1 = (V 1,E
More informationInduced Saturation of Graphs
Induced Saturation of Graphs Maria Axenovich a and Mónika Csikós a a Institute of Algebra and Geometry, Karlsruhe Institute of Technology, Englerstraße 2, 76128 Karlsruhe, Germany Abstract A graph G is
More informationOn a hypergraph matching problem
On a hypergraph matching problem Noga Alon Raphael Yuster Abstract Let H = (V, E) be an r-uniform hypergraph and let F 2 V. A matching M of H is (α, F)- perfect if for each F F, at least α F vertices of
More informationDiscrete Mathematics. The edge spectrum of the saturation number for small paths
Discrete Mathematics 31 (01) 68 689 Contents lists available at SciVerse ScienceDirect Discrete Mathematics journal homepage: www.elsevier.com/locate/disc The edge spectrum of the saturation number for
More information< k 2n. 2 1 (n 2). + (1 p) s) N (n < 1
List of Problems jacques@ucsd.edu Those question with a star next to them are considered slightly more challenging. Problems 9, 11, and 19 from the book The probabilistic method, by Alon and Spencer. Question
More informationExtremal Functions for Graph Linkages and Rooted Minors. Paul Wollan
Extremal Functions for Graph Linkages and Rooted Minors A Thesis Presented to The Academic Faculty by Paul Wollan In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy School of
More informationThe structure of bull-free graphs I three-edge-paths with centers and anticenters
The structure of bull-free graphs I three-edge-paths with centers and anticenters Maria Chudnovsky Columbia University, New York, NY 10027 USA May 6, 2006; revised March 29, 2011 Abstract The bull is the
More informationBalanced bipartitions of graphs
2010.7 - Dedicated to Professor Feng Tian on the occasion of his 70th birthday Balanced bipartitions of graphs Baogang Xu School of Mathematical Science, Nanjing Normal University baogxu@njnu.edu.cn or
More informationarxiv: v2 [math.co] 20 Jun 2018
ON ORDERED RAMSEY NUMBERS OF BOUNDED-DEGREE GRAPHS MARTIN BALKO, VÍT JELÍNEK, AND PAVEL VALTR arxiv:1606.0568v [math.co] 0 Jun 018 Abstract. An ordered graph is a pair G = G, ) where G is a graph and is
More informationarxiv: v1 [math.co] 28 Jan 2019
THE BROWN-ERDŐS-SÓS CONJECTURE IN FINITE ABELIAN GROUPS arxiv:191.9871v1 [math.co] 28 Jan 219 JÓZSEF SOLYMOSI AND CHING WONG Abstract. The Brown-Erdős-Sós conjecture, one of the central conjectures in
More informationThis is a repository copy of Chromatic index of graphs with no cycle with a unique chord.
This is a repository copy of Chromatic index of graphs with no cycle with a unique chord. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/74348/ Article: Machado, RCS, de
More informationIndependent Transversals in r-partite Graphs
Independent Transversals in r-partite Graphs Raphael Yuster Department of Mathematics Raymond and Beverly Sackler Faculty of Exact Sciences Tel Aviv University, Tel Aviv, Israel Abstract Let G(r, n) denote
More informationColorings of uniform hypergraphs with large girth
Colorings of uniform hypergraphs with large girth Andrey Kupavskii, Dmitry Shabanov Lomonosov Moscow State University, Moscow Institute of Physics and Technology, Yandex SIAM conference on Discrete Mathematics
More informationA taste of perfect graphs
A taste of perfect graphs Remark Determining the chromatic number of a graph is a hard problem, in general, and it is even hard to get good lower bounds on χ(g). An obvious lower bound we have seen before
More informationProbabilistic Proofs of Existence of Rare Events. Noga Alon
Probabilistic Proofs of Existence of Rare Events Noga Alon Department of Mathematics Sackler Faculty of Exact Sciences Tel Aviv University Ramat-Aviv, Tel Aviv 69978 ISRAEL 1. The Local Lemma In a typical
More informationRECAP: Extremal problems Examples
RECAP: Extremal problems Examples Proposition 1. If G is an n-vertex graph with at most n edges then G is disconnected. A Question you always have to ask: Can we improve on this proposition? Answer. NO!
More information1 Notation. 2 Sergey Norin OPEN PROBLEMS
OPEN PROBLEMS 1 Notation Throughout, v(g) and e(g) mean the number of vertices and edges of a graph G, and ω(g) and χ(g) denote the maximum cardinality of a clique of G and the chromatic number of G. 2
More informationEQUITABLE COLORING OF SPARSE PLANAR GRAPHS
EQUITABLE COLORING OF SPARSE PLANAR GRAPHS RONG LUO, D. CHRISTOPHER STEPHENS, AND GEXIN YU Abstract. A proper vertex coloring of a graph G is equitable if the sizes of color classes differ by at most one.
More informationThe typical structure of maximal triangle-free graphs
The typical structure of maximal triangle-free graphs József Balogh Hong Liu Šárka Petříčková Maryam Sharifzadeh September 3, 2018 arxiv:1501.02849v1 [math.co] 12 Jan 2015 Abstract Recently, settling a
More informationarxiv: v2 [math.co] 19 Jun 2018
arxiv:1705.06268v2 [math.co] 19 Jun 2018 On the Nonexistence of Some Generalized Folkman Numbers Xiaodong Xu Guangxi Academy of Sciences Nanning 530007, P.R. China xxdmaths@sina.com Meilian Liang School
More informationProbabilistic Method. Benny Sudakov. Princeton University
Probabilistic Method Benny Sudakov Princeton University Rough outline The basic Probabilistic method can be described as follows: In order to prove the existence of a combinatorial structure with certain
More informationSome Problems in Graph Ramsey Theory. Andrey Vadim Grinshpun
Some Problems in Graph Ramsey Theory by Andrey Vadim Grinshpun Submitted to the Department of Mathematics in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mathematics
More informationA necessary and sufficient condition for the existence of a spanning tree with specified vertices having large degrees
A necessary and sufficient condition for the existence of a spanning tree with specified vertices having large degrees Yoshimi Egawa Department of Mathematical Information Science, Tokyo University of
More informationAn Algorithmic Hypergraph Regularity Lemma
An Algorithmic Hypergraph Regularity Lemma Brendan Nagle Vojtěch Rödl Mathias Schacht October 14, 2015 Abstract Szemerédi s Regularity Lemma [22, 23] is a powerful tool in graph theory. It asserts that
More informationVertex colorings of graphs without short odd cycles
Vertex colorings of graphs without short odd cycles Andrzej Dudek and Reshma Ramadurai Department of Mathematical Sciences Carnegie Mellon University Pittsburgh, PA 1513, USA {adudek,rramadur}@andrew.cmu.edu
More informationCombinatorics and Optimization 442/642, Fall 2012
Compact course notes Combinatorics and Optimization 44/64, Fall 0 Graph Theory Contents Professor: J. Geelen transcribed by: J. Lazovskis University of Waterloo December 6, 0 0. Foundations..............................................
More informationNew Results on Graph Packing
Graph Packing p.1/18 New Results on Graph Packing Hemanshu Kaul hkaul@math.uiuc.edu www.math.uiuc.edu/ hkaul/. University of Illinois at Urbana-Champaign Graph Packing p.2/18 Introduction Let G 1 = (V
More information1.3 Vertex Degrees. Vertex Degree for Undirected Graphs: Let G be an undirected. Vertex Degree for Digraphs: Let D be a digraph and y V (D).
1.3. VERTEX DEGREES 11 1.3 Vertex Degrees Vertex Degree for Undirected Graphs: Let G be an undirected graph and x V (G). The degree d G (x) of x in G: the number of edges incident with x, each loop counting
More informationCycles in 4-Connected Planar Graphs
Cycles in 4-Connected Planar Graphs Guantao Chen Department of Mathematics & Statistics Georgia State University Atlanta, GA 30303 matgcc@panther.gsu.edu Genghua Fan Institute of Systems Science Chinese
More informationAN IMPROVED ERROR TERM FOR MINIMUM H-DECOMPOSITIONS OF GRAPHS. 1. Introduction We study edge decompositions of a graph G into disjoint copies of
AN IMPROVED ERROR TERM FOR MINIMUM H-DECOMPOSITIONS OF GRAPHS PETER ALLEN*, JULIA BÖTTCHER*, AND YURY PERSON Abstract. We consider partitions of the edge set of a graph G into copies of a fixed graph H
More informationList of Theorems. Mat 416, Introduction to Graph Theory. Theorem 1 The numbers R(p, q) exist and for p, q 2,
List of Theorems Mat 416, Introduction to Graph Theory 1. Ramsey s Theorem for graphs 8.3.11. Theorem 1 The numbers R(p, q) exist and for p, q 2, R(p, q) R(p 1, q) + R(p, q 1). If both summands on the
More informationAALBORG UNIVERSITY. Total domination in partitioned graphs. Allan Frendrup, Preben Dahl Vestergaard and Anders Yeo
AALBORG UNIVERSITY Total domination in partitioned graphs by Allan Frendrup, Preben Dahl Vestergaard and Anders Yeo R-2007-08 February 2007 Department of Mathematical Sciences Aalborg University Fredrik
More informationDisjoint Subgraphs in Sparse Graphs 1
Disjoint Subgraphs in Sparse Graphs 1 Jacques Verstraëte Department of Pure Mathematics and Mathematical Statistics Centre for Mathematical Sciences Wilberforce Road Cambridge CB3 OWB, UK jbav2@dpmms.cam.ac.uk
More informationMatchings in hypergraphs of large minimum degree
Matchings in hypergraphs of large minimum degree Daniela Kühn Deryk Osthus Abstract It is well known that every bipartite graph with vertex classes of size n whose minimum degree is at least n/2 contains
More informationGraph coloring, perfect graphs
Lecture 5 (05.04.2013) Graph coloring, perfect graphs Scribe: Tomasz Kociumaka Lecturer: Marcin Pilipczuk 1 Introduction to graph coloring Definition 1. Let G be a simple undirected graph and k a positive
More informationMonochromatic subgraphs of 2-edge-colored graphs
Monochromatic subgraphs of 2-edge-colored graphs Luke Nelsen, Miami University June 10, 2014 Abstract Lehel conjectured that for all n, any 2-edge-coloring of K n admits a partition of the vertex set into
More informationTHE ASYMPTOTIC NUMBER OF TRIPLE SYSTEMS NOT CONTAINING A FIXED ONE
THE ASYMPTOTIC NUMBER OF TRIPLE SYSTEMS NOT CONTAINING A FIXED ONE BRENDAN NAGLE AND VOJTĚCH RÖDL Abstract. For a fixed 3-uniform hypergraph F, call a hypergraph F-free if it contains no subhypergraph
More information