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Erdős problem 1119

Let m\mathfrak{m} be an infinite cardinal with 0<m<c=20\aleph_0 < \mathfrak{m} < \mathfrak{c} = 2^{\aleph_0}. Let {fα}\{f_\alpha\} be a family of entire functions such that, for every z0Cz_0 \in \mathbb{C}, there are at most m\mathfrak{m} distinct values of fα(z0)f_\alpha(z_0). Must {fα}\{f_\alpha\} have cardinality at most m\mathfrak{m}?

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1119.lean

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Let m\mathfrak{m} be an infinite cardinal with 0<m<c=20\aleph_0 < \mathfrak{m} < \mathfrak{c} = 2^{\aleph_0}. Let {fα}\{f_\alpha\} be a family of entire functions such that, for every z0Cz_0 \in \mathbb{C}, there are at most m\mathfrak{m} distinct values of fα(z0)f_\alpha(z_0). Must {fα}\{f_\alpha\} have cardinality at most m\mathfrak{m}?

This is Problem 2.46 in [Ha74], where it is attributed to Erdős. The question is independent of ZFC, so the headline statement carries answer(sorry): it is neither provable nor refutable from the usual axioms of set theory.

The answer is yes if m+<c\mathfrak{m}^+ < \mathfrak{c} (see erdos_1119.variants.easy_case), so the question reduces to the case m+=c\mathfrak{m}^+ = \mathfrak{c}, where it is undecidable: Kumar and Shelah [KuSh17] produced a model of c=2\mathfrak{c} = \aleph_2 in which the answer is yes (with m=1\mathfrak{m} = \aleph_1), while Schilhan and Weinert [ScWe24] produced a different model of c=2\mathfrak{c} = \aleph_2 in which the answer is no.

FormalConjectures/ErdosProblems/1119.leanErdos1119.erdos_11196 linesExact file
True  ∀ (m : Cardinal.{0}),    Cardinal.aleph0 < m      m < Cardinal.continuum        ∀ (F : Set (ℂ → ℂ)),          (∀ fF, Differentiablef) → (∀ (z₀ : ℂ), Cardinal.mk ↑{y | ∃ fF, f z₀ = y} ≤ m) → Cardinal.mkFm
SolvedStatement only, no proof

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