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Erdős Problem #1034

DISPROVED LEANdatabase updated 2025-12-04

The statement as posed is false. A solution has also been checked by machine, in Lean.

What the community database records, not our verdict. erdosproblems.com no longer shows statuses (why).

`JoinedToTwo G T Y` holds when every vertex of `Y` is joined to at least two (distinct) vertices of `T`.

Let \(G\) be a graph on \(n\) vertices with \(>n^2/4\) many edges. Must there be a triangle \(T\) in \(G\) and vertices \(y_1,\ldots,y_t\), where \(t>(\frac{1}{2}-o(1))n\), such that every \(y_i\) is joined to at least two vertices of \(T\)? A conjecture of Erdős and Faudree; a stronger version of [905]. This has been solved in the negative by Ma and Tang [MaTa25], who construct a graph with \(n\) vertices and \(>n^2/4\) edges in which every triangle has at most \((2-(5/2)^{1/2}+o(1))n\) vertices adjacent to at least two of its vertices (note that \(2-(5/2)^{1/2}\approx 0.4189\)).
Statement as formalized in Formal Conjectures (Google DeepMind, Apache-2.0) · their label: research solved · 3 further variants / known partial results in the Lean file. The authoritative wording is on erdosproblems.com/1034.
Prizenone
Topicsgraph theory
Statement in LeanFormal Conjectures
Solution in Leanyes
Original pageerdosproblems.com/1034
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