A rainbow blow-up lemma for almost optimally bounded edge-colourings
Pith reviewed 2026-05-24 17:26 UTC · model grok-4.3
The pith
A rainbow blow-up lemma holds for edge-colorings that are almost optimally bounded.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We prove a rainbow version of the blow-up lemma of Komlós, Sárközy and Szemerédi that applies to almost optimally bounded colourings. A corollary of this is that there exists a rainbow copy of any bounded-degree spanning subgraph H in a quasirandom host graph G, assuming that the edge-colouring of G fulfills a boundedness condition that is asymptotically best possible. This has many applications beyond rainbow colourings, for example to graph decompositions, orthogonal double covers and graph labellings.
What carries the argument
The rainbow blow-up lemma, which embeds rainbow copies of bounded-degree graphs into dense quasirandom hosts whose edges satisfy an asymptotically tight per-color bound.
If this is right
- Any quasirandom graph whose edges are colored under the stated boundedness condition contains a rainbow copy of every bounded-degree spanning subgraph.
- The lemma supplies rainbow versions of many classical embedding results used in graph decompositions.
- It yields new existence statements for orthogonal double covers via the same embedding mechanism.
- It produces rainbow embeddings that can be repurposed for certain graph-labelling problems.
Where Pith is reading between the lines
- The same boundedness condition may suffice for rainbow versions of other embedding lemmas that currently require stricter color restrictions.
- One could check the result numerically on small random regular graphs to see how close the boundedness threshold must be in practice.
- The technique might extend to hypergraph embeddings or to settings where only a fraction of the edges need to be rainbow.
Load-bearing premise
The edge-colouring must obey a per-color boundedness condition that is asymptotically the strongest possible for the embedding statement to remain true.
What would settle it
An explicit quasirandom graph together with an edge-coloring in which some color appears on more than the allowed number of edges (by a constant factor) yet no rainbow copy of a fixed bounded-degree spanning subgraph exists would refute the claim.
Figures
read the original abstract
A subgraph of an edge-coloured graph is called rainbow if all its edges have different colours. We prove a rainbow version of the blow-up lemma of Koml\'os, S\'ark\"ozy and Szemer\'edi that applies to almost optimally bounded colourings. A corollary of this is that there exists a rainbow copy of any bounded-degree spanning subgraph $H$ in a quasirandom host graph $G$, assuming that the edge-colouring of $G$ fulfills a boundedness condition that is asymptotically best possible. This has many applications beyond rainbow colourings, for example to graph decompositions, orthogonal double covers and graph labellings.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proves a rainbow version of the Komlós–Sárközy–Szemerédi blow-up lemma that holds for edge-colourings satisfying an asymptotically optimal boundedness condition. As a corollary, any bounded-degree spanning subgraph H admits a rainbow copy in a quasirandom host G under this colouring condition. The result is stated to have further applications to graph decompositions, orthogonal double covers and graph labellings.
Significance. If the central lemma holds, the work supplies a flexible embedding tool for rainbow problems at the natural density threshold. The optimality claim on the boundedness condition strengthens the result relative to earlier rainbow blow-up statements and directly supports the corollary on spanning subgraphs in quasirandom graphs.
minor comments (2)
- [Abstract] The abstract refers to an 'almost optimally bounded' colouring without stating the precise quantitative condition; the introduction or statement of the main lemma should give the exact bound (e.g., maximum colour degree o(n) or similar) so that the optimality claim can be verified immediately.
- [Section 2] Notation for the host graph G, the colouring, and the blow-up parameters should be introduced uniformly in §2 before the statement of the main lemma; occasional reuse of symbols from the classical blow-up lemma risks confusion.
Simulated Author's Rebuttal
We thank the referee for their positive evaluation of the manuscript, the supportive summary of its contributions, and the recommendation for minor revision. No major comments were raised in the report.
Circularity Check
No significant circularity; direct proof of extended lemma
full rationale
The paper states a direct proof of a rainbow blow-up lemma extending the Komlós-Sárközy-Szemerédi result to almost optimally bounded edge-colourings, with a corollary for rainbow spanning subgraphs in quasirandom hosts. No self-definitional relations, fitted inputs renamed as predictions, load-bearing self-citations, uniqueness theorems imported from the authors' prior work, smuggled ansatzes, or renamings of known results appear in the abstract or claim structure. The boundedness condition is presented as an external asymptotic optimality assumption rather than an internal fit. The derivation chain is therefore self-contained as a mathematical existence proof.
Axiom & Free-Parameter Ledger
axioms (2)
- standard math The blow-up lemma of Komlós, Sárközy and Szemerédi
- domain assumption Quasirandomness of the host graph G
Reference graph
Works this paper leans on
-
[1]
A. Adamaszek, P. Allen, C. Grosu, and J. Hladk´ y, Almost all trees are almost graceful , arXiv:1608.01577 (2016)
- [2]
-
[3]
Perfectly packing graphs with bounded degeneracy and many leaves
P. Allen, J. B¨ ottcher, D. Clemens, and A. Taraz, Perfectly packing graphs with bounded degeneracy and many leaves, arXiv:1906.11558 (2019)
work page internal anchor Pith review Pith/arXiv arXiv 1906
- [4]
- [5]
-
[6]
J. B¨ ottcher, Y. Kohayakawa, and A. Procacci, Properly coloured copies and rainbow copies of large graphs with small maximum degree , Random Structures Algorithms 40 (2012), 425–436
work page 2012
-
[7]
J. B¨ ottcher, Y. Kohayakawa, A. Taraz, and A. W¨ urfl, An extension of the blow-up lemma to arrangeable graphs, SIAM J. Discrete Math. 29 (2015), 962–1001
work page 2015
-
[8]
J. B¨ ottcher, M. Schacht, and A. Taraz, Proof of the bandwidth conjecture of Bollob´ as and Koml´ os, Math. Ann. 343 (2009), 175–205
work page 2009
-
[9]
M. Coulson and G. Perarnau, Rainbow matchings in Dirac bipartite graphs , Random Structures Algorithms (to appear)
-
[10]
Csaba, On the Bollob´ as-Eldridge conjecture for bipartite graphs , Combin
B. Csaba, On the Bollob´ as-Eldridge conjecture for bipartite graphs , Combin. Probab. Comput. 16 (2007), 661–691
work page 2007
-
[11]
M. Drmota and A. Llad´ o, Almost every tree with m edges decomposes K2m,2m, Combin. Probab. Comput. 23 (2014), 50–65
work page 2014
-
[12]
R. A. Duke, H. Lefmann, and V. R¨ odl, A fast approximation algorithm for computing the frequenci es of subgraphs in a given graph , SIAM J. Comput. 24 (1995), 598–620
work page 1995
- [13]
-
[14]
P. Erd˝ os, J. Neˇ setˇ ril, and V. R¨ odl,On some problems related to partitions of edges of a graph , Graphs and other combinatorial topics, Teubner-Texte Math. 59, Teubn er, 1983, pp. 54–63
work page 1983
-
[15]
J. A. Gallian, A dynamic survey of graph labeling , Electron. J. Combin. 5 (1998), Dynamic Survey 6, 43
work page 1998
-
[16]
S. Glock and F. Joos, A rainbow blow-up lemma , arXiv:1802.07700 (2018). 28 S. EHARD, S. GLOCK, AND F. JOOS
work page internal anchor Pith review Pith/arXiv arXiv 2018
- [17]
- [18]
- [19]
-
[20]
R. L. Graham and N. J. A. Sloane, On additive bases and harmonious graphs , SIAM J. Algebraic Discrete Methods 1 (1980), 382–404
work page 1980
-
[21]
H.-D. O. F. Gronau, R. C. Mullin, and A. Rosa, Orthogonal double covers of complete graphs by trees , Graphs Combin. 13 (1997), 251–262
work page 1997
-
[22]
A. Hajnal and E. Szemer´ edi, Proof of a conjecture of Erd˝ os, In: Combinatorial Theory and its Applications II (P. Erd˝ os, A. R´ enyi, and V.T. S´ os, eds.), North Holland, 1970, pp. 601–623
work page 1970
- [23]
-
[24]
F. Joos, J. Kim, D. K¨ uhn, and D. Osthus, Optimal packings of bounded degree trees , J. Eur. Math. Soc. (to appear)
-
[25]
Keevash, A hypergraph blow-up lemma , Random Structures Algorithms 39 (2011), 275–376
P. Keevash, A hypergraph blow-up lemma , Random Structures Algorithms 39 (2011), 275–376
work page 2011
- [26]
-
[27]
, The existence of designs II , arXiv:1802.05900 (2018)
work page internal anchor Pith review Pith/arXiv arXiv 2018
- [28]
-
[29]
J. Kim, D. K¨ uhn, D. Osthus, and M. Tyomkyn, A blow-up lemma for approximate decompositions , Trans. Amer. Math. Soc. 371 (2019), 4655–4742
work page 2019
-
[30]
J. Koml´ os, G. N. S´ ark¨ ozy, and E. Szemer´ edi,Blow-up lemma , Combinatorica 17 (1997), 109–123
work page 1997
-
[31]
Graph Theory 29 (1998), 167–176
, On the P´ osa-Seymour conjecture, J. Graph Theory 29 (1998), 167–176
work page 1998
-
[32]
, Proof of the Seymour conjecture for large graphs , Ann. Comb. 2 (1998), 43–60
work page 1998
-
[33]
, Proof of the Alon-Yuster conjecture , Discrete Math. 235 (2001), 255–269
work page 2001
-
[34]
Kotzig, On certain vertex-valuations of finite graphs , Utilitas Math
A. Kotzig, On certain vertex-valuations of finite graphs , Utilitas Math. 4 (1973), 261–290
work page 1973
-
[35]
D. K¨ uhn and D. Osthus, The minimum degree threshold for perfect graph packings , Combinatorica 29 (2009), 65–107
work page 2009
-
[36]
, Hamilton decompositions of regular expanders: A proof of Ke lly’s conjecture for large tournaments , Adv. Math. 237 (2013), 62–146
work page 2013
-
[37]
C. McDiarmid, On the method of bounded differences , Surveys in combinatorics, 1989 (Norwich, 1989), London Math. Soc. Lecture Note Ser. 141, Cambridge Univ. Pre ss, 1989, pp. 148–188
work page 1989
-
[38]
R. Montgomery, A. Pokrovskiy, and B. Sudakov, Decompositions into spanning rainbow structures , Proc. Lond. Math. Soc. 119 (2019), 899–959
work page 2019
-
[39]
, Embedding rainbow trees with applications to graph labelli ng and decomposition , J. Eur. Math. Soc. (to appear)
-
[40]
R¨ odl, On a packing and covering problem , European J
V. R¨ odl, On a packing and covering problem , European J. Combin. 6 (1985), 69–78
work page 1985
-
[41]
V. R¨ odl and A. Ruci´ nski,Perfect matchings in ǫ-regular graphs and the blow-up lemma , Combinatorica 19 (1999), 437–452
work page 1999
-
[42]
Rosa, On certain valuations of the vertices of a graph , Theory of Graphs (Internat
A. Rosa, On certain valuations of the vertices of a graph , Theory of Graphs (Internat. Sympos., Rome, 1966), Gordon and Breach, New York; Dunod, Paris, 1967, pp. 3 49–355
work page 1966
-
[43]
˙Zak, Harmonious order of graphs , Discrete Math
A. ˙Zak, Harmonious order of graphs , Discrete Math. 309 (2009), 6055–6064. (S. Ehard) Institut f ¨ur Optimierung und Operations Research, Universit ¨at Ulm, Ulm, Germany E-mail address : stefan.ehard@uni-ulm.de (S. Glock, F. Joos) School of Mathematics, University of Birmingham, Edgbasto n, Birmingham, B15 2TT, United Kingdom E-mail address : [s.glock, f...
work page 2009
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