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Erdős problem 70

Erdős Problem 70: Let c\mathfrak{c} be the cardinality of the continuum, let β\beta be a countable ordinal, and let 2≤n<ω2 \le n < \omega. Is it true that c→(β,n)23\mathfrak{c} \to (\beta, n)^3_2?

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6 retained statements36c6d0fef71a

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FormalConjectures/ErdosProblems/

70.lean

Retained formal statement5 of 6

First open case beyond Erdős–Rado: c→(ω⋅2,4)23\mathfrak{c} \to (\omega \cdot 2, 4)^3_2.

Erdős and Rado proved c→(ω+n,4)23\mathfrak{c} \to (\omega + n, 4)^3_2 for every finite n≥2n \ge 2 (see erdos_rado), which covers all red ordinals below ω⋅2=ω+ω\omega \cdot 2 = \omega + \omega. This variant asks whether the result extends to β=ω⋅2\beta = \omega \cdot 2, the simplest countable ordinal not covered by their theorem.

FormalConjectures/ErdosProblems/70.leanErdos70.erdos_70.variants.omega_times_two_four1 lineExact file
True ↔ Erdos70.OrdinalCardinalRamsey3 Cardinal.continuum.ord (Ordinal.omega0 * 2) 4
OpenStatement only, no proof