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Erdős problem 1167

Erdős Problem 1167. Let r2r \geq 2 be finite, γ2\gamma \geq 2, and λ\lambda be an infinite cardinal. Let κα\kappa_\alpha be cardinals for all α<γ\alpha < \gamma. Is it true that 2λ(κα+1)α<γr+12^\lambda \to (\kappa_\alpha + 1)_{\alpha < \gamma}^{r+1} implies λ(κα)α<γr?\lambda \to (\kappa_\alpha)_{\alpha < \gamma}^r? Here ++ means cardinal addition, so that κα+1=κα\kappa_\alpha + 1 = \kappa_\alpha if κα\kappa_\alpha is infinite.

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8 retained statements2415f78e850a

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FormalConjectures/ErdosProblems/

1167.lean

Retained formal statement8 of 8

**r=2r = 2 case.** The stepping-down from 3-uniform to 2-uniform partition relations: 2λ(κα+1)α<γ32^\lambda \to (\kappa_\alpha + 1)_{\alpha<\gamma}^3 implies λ(κα)α<γ2\lambda \to (\kappa_\alpha)_{\alpha<\gamma}^2. Generalises the classical Erdős–Rado stepping-up/down theorem for pairs.

FormalConjectures/ErdosProblems/1167.leanErdos1167.erdos_1167.variants.r_eq_two7 linesExact file
∀ (lam : Cardinal.{u}),  Cardinal.aleph0lam    ∀ (γ : Ordinal.{u}),      2 ≤ γ →        ∀ (κ : γ.ToTypeCardinal.{u}),          (Combinatorics.cardinalPartitionRel (2 ^ lam) 3 γ fun α => κ α + 1) →            Combinatorics.cardinalPartitionRel lam 2 γ κ
OpenStatement only, no proof

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