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Erdős Problem #78

OPENdatabase updated 2025-08-31

No proof or disproof is known, and it isn't known whether a finite computation could settle it.

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The graph on `Fin n` described by an adjacency oracle `adj`. Two distinct vertices `u` and `v` are adjacent if `adj (1ⁿ, u, v)` or `adj (1ⁿ, v, u)` is `true`. The number of vertices is given in unary, as the list `List.replicate n true`. So if `adj` is computable in polynomial time, then the whole graph on `n` vertices is computable in time polynomial in `n`. This is the notion of a *weakly explicit* family of graphs; compare `stronglyExplicitGraph`.

The graph on `Fin n` described by an adjacency oracle `adj` which receives `n` in binary. Two distinct vertices `u` and `v` are adjacent if `adj (n, u, v)` or `adj (n, v, u)` is `true`. If `adj` is computable in polynomial time, then each adjacency query is answered in time polynomial in \(\log n\). This is the notion of a *strongly explicit* family of graphs, which is what "explicit Ramsey graph" usually means in the literature (e.g. [Co15], [Li23b]). Compare `explicitGraph`, where only time poly

The graph `G` has no clique and no independent set with `m` vertices.

Let \(R(k)\) be the Ramsey number for \(K_k\). Give a constructive proof that \(R(k) > C^k\) for some constant \(C > 1\). Equivalently, give an explicit construction of graphs on \(n\) vertices which contain no clique and no independent set of size \(\geq c \log n\), for some constant \(c > 0\). We formalise "explicit" as: the adjacency relation of the graph on \(n\) vertices is decided by a single algorithm that runs in time polynomial in \(n\) (see `explicitGraph`). This is the weakest reasonable notion ("weakly explicit"); even this is open. The strongly explicit version, with time polynomial in \(\log n\), is `erdos_78.variants.strongly_explicit`. This problem is #4 in Ramsey Theory in the graphs problem collection.
Statement as formalized in Formal Conjectures (Google DeepMind, Apache-2.0) · their label: research open · 6 further variants / known partial results in the Lean file. The authoritative wording is on erdosproblems.com/78.
Prize$100
Topicsgraph theory, ramsey theory
Statement in LeanFormal Conjectures
Solution in Leanno
OEISA059442
Original pageerdosproblems.com/78
WORKING REPORT BY THIS SITE · JUL 26, 2026

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Exact post-1601 Paley values (including \(\omega(P_{1669})=\alpha(P_{1669})=13\)) and the entropy-\(\log m+O(1)\) reduction are verified, but the required uniform strongly explicit family remains open

PARTIAL