All open problems
Source labels openChecked July 26, 2026

Erdős ProblemsMathematical logic

Erdős Problem 70

First open case beyond Erdős–Rado*: c(ω2,4)23\mathfrak{c} \to (\omega \cdot 2, 4)^3_2.

Mathematical statement

First open case beyond Erdős–Rado*: c(ω2,4)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 n2n \ge 2 (see erdos_rado), which covers all red ordinals below ω2=ω+ω\omega \cdot 2 = \omega + \omega. This variant asks whether the result extends to β=ω2\beta = \omega \cdot 2, the simplest countable ordinal not covered by their theorem.

Statement source: Erdős Problems statement material

Statement terms: Source-specific

Source-specific terms. Therefore does not assert reuse rights beyond attributed display.

Statement artifacts, not proofs

These records expose exact Lean propositions and statement-only wrappers. Defining a proposition does not supply a proof of it. A placeholder-bearing target also contains no proof. Elaboration checks syntax and types; it does not certify that a formalization perfectly captures every nuance of the informal problem.

Pinned Lean formulation 1

omega_times_two_four

Canonical source
Complete statement target, proof intentionally absentLean 4
theorem omega_times_two_four :    answer(sorry)  OrdinalCardinalRamsey3 (𝔠).ord (ω * 2) 4 := by  sorry
Statement source
Formal Conjectures
Lean version
v4.27.0
Placeholder
Present; no proof artifact
Source evidence
Pinned source index
Fidelity review
Community formulation

References