Problems
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In the Frankl-Pach-Erdős circle of VC-dimension problems, the first arXiv version of the paper posed the k=3 case of a witness construction question. ChatGPT 5.4 Pro answered it; the published construction generalizes the model's response,…
Is the number of nonnesting permutations of 1,1,…,n,n avoiding both 1132 and 3312 equal to 3^n - 3 · 2^n-1 + 1 for every n ≥ 1?
VibeMathed records no statement for this problem. See erdosproblems.com for the original.
An asymptotic formula for p(k), the limiting probability that a random permutation has an invariant set of size k: it is asymptotically k^-δ(1+o(1)) times a smooth positive function, sharpening a line of estimates running through…
The multivariate independence polynomial is the partition function of the hard-core model with per-vertex fugacities. The paper proves a lower bound extending to the multivariate setting a result Tao proved in the univariate case, and…
For positive integers d and k, let n_k(d) be the maximum order of a graph of maximum degree at most d and diameter at most k. It is shown that lim_d → ∞n_k(d)/d^k = 1 for every fixed k, thereby resolving the asymptotic degree-diameter…
Erdos Problem #593 asks which finite triple systems occur in every uncountably chromatic triple system. The answer is exactly the class generated from private-vertex expansions of finite bipartite graphs by finite disjoint unions and…
Treglown conjectured, in a complementary form, that for every positive integer k every digraph D with mind^+(v), d^-(v) ≤ k-1 for all v has an equitable acyclic k-colouring. This implies the acyclic colouring versions of the…
With N = 2^k - 1 and wt(n) the binary Hamming weight, Tu and Deng conjectured that for every 1 ≤ t ≤ N-1 at most 2^k-1 pairs (a,b) satisfy a + b ≡ t pmod N and wt(a) + wt(b) < k. Proved in full.
A graph G on n vertices with k edges is t-edge-balanced if every graph on n vertices with t edges is contained in exactly the same number of subgraphs of K_n isomorphic to G. Infinite families were known for t = 2, but no example was known…
Boots and Royle, and independently Cao and Vince, conjectured that the join of an edge with a path on n-2 vertices is the unique planar graph of maximum adjacency spectral radius for every n ≥ 9. Tait and Tobin proved it for sufficiently…
VibeMathed records no statement for this problem. See erdosproblems.com for the original.
Frankl, Peng, Rodl and Talbot asked in 2007 whether the set of Turan densities of families of r-graphs contains intervals. It does: for every r ≥ 3 the set contains non-degenerate intervals, including one of the form [1-δ_r, 1].
VibeMathed records no statement for this problem. See erdosproblems.com for the original.
If W(k) is the least N such that every two-colouring of 1, …, N contains a monochromatic k-term arithmetic progression, must W(k+1) - W(k) → ∞?
Can the edges of a finite connected multigraph, given a closed eulerian trail, be partitioned into circuits so that no circuit contains two edges used consecutively in the trail? The proof in fact four-colours the edges to satisfy the…
The quartet distance counts the four-leaf subsets on which two binary phylogenetic trees display different topologies. Bandelt and Dress conjectured the maximum over trees on n leaves. Proved: it is (2/3 + o(1))binomn4, by reducing…
Coble and Barg introduced binary Coxeter codes, the span of indicators of standard cosets of fixed rank in a finite Coxeter system, generalizing Reed-Muller codes, and proposed a conjectural value for the minimum distance of a general…
Donner proved in 1992 that the list color function P_ℓ(G,k) equals the chromatic polynomial P(G,k) once k is large. Kaul and Mudrock asked whether the analogue holds for Hanlon's unlabeled chromatic polynomial, and could not settle even…
Gao, Huo and Ma asked whether for every fixed k ≥ 3 there is a function f_k(n) → ∞ such that every n-vertex (k+1)-critical graph contains f_k(n) consecutive cycle lengths. The paper settles this and two related problems on cycle lengths…