The board / set theory / #1167
Erdős Problem #1167
OPENdatabase updated 2026-01-23
No proof or disproof is known, and it isn't known whether a finite computation could settle it.
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**Erdős Problem 1167.** Let \(r \geq 2\) be finite, \(\gamma \geq 2\), and \(\lambda\) be an infinite cardinal. Let \(\kappa_\alpha > r\) be cardinals for all \(\alpha < \gamma\). Is it true that \[2^\lambda \to (\kappa_\alpha + 1)_{\alpha < \gamma}^{r+1}\] implies \[\lambda \to (\kappa_\alpha)_{\alpha < \gamma}^r?\] Here \(+\) means cardinal addition, so that \(\kappa_\alpha + 1 = \kappa_\alpha\) if \(\kappa_\alpha\) is infinite. A problem of Erdős, Hajnal, and Rado.
Statement as formalized in Formal Conjectures (Google DeepMind, Apache-2.0) · their label: research open · 4 further variants / known partial results in the Lean file. The authoritative wording is on erdosproblems.com/1167.Prizenone
Topicsset theory, ramsey theory
Statement in LeanFormal Conjectures
Solution in Leanno
Original pageerdosproblems.com/1167
Attempts
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