Research notes on every problem, and a library of the papers behind them. Built from the open erdos repository.
Updated
Claim. Let with $\operatorname{cf}(\lambda)> \omega_1$, and add Cohen reals. In the extension, every family of pairwise distinct entire functions has a point at which it takes distinct values. In particular, starting from , the extension has and every family of entire functions taking at most values at each point has at most members, so the question of Problem 1119 has a positive answer there for its only admissible cardinal, . This is Theorem 2.1 of the preprint Sh:1078 in Shelah's archive (version of 2017-01-05), which dates the page; the paper was published as Ashutosh Kumar and Saharon Shelah, On a question about families of entire functions, Fund. Math. 239 (2017), no. 3, 279--288, and the theorem numbering of the published version was not compared. The source card records the statements.
Covers. The case with the continuum hypothesis failing: in the model of Theorem 2.1 built from , the cardinal has and the answer is yes. For the literal statement, non-refutability needs no such model: under the continuum hypothesis no cardinal satisfies , so the statement holds vacuously in every model of CH, such as Gödel's constructible universe, and whenever the answer is yes by Erdős's counting argument. What this theorem adds is a positive answer in a model of the negation of CH in the hard case . Independence of that case needs both this model and Schilhan and Weinert's result, a model with in which the answer for is no. The paper's Theorem 3.1 also gives a model of the negation of the continuum hypothesis with a family of entire functions taking fewer than values at every point, but there is singular and the value sets have no uniform bound below , so that theorem does not answer the problem's question for a single .
Argument, in outline. A Cohen-generic point avoids every meager set coded before it, and two distinct entire functions agree on at most a countable set; the authors use both to show that distinct functions cannot all take few values at . The proof is not reconstructed on this page.
Context. Erdős showed in 1964 (source card) that the countable case depends on the continuum hypothesis, and his counting argument gives a positive answer whenever $\mathfrak m^+<\mathfrak c$, which Hayman's 1974 problem list calls easy; the open case is , which this model realizes with and .
Acceptance. The result appeared in a refereed journal, Fundamenta
Mathematicae, in 2017, the refereed evidence; the preprint was not
compared with the published version. The site's curator, Thomas Bloom,
marks the problem INDEPENDENT and records in the commentary that Kumar and
Shelah gave a model with in which the answer is yes
for : that curator credit is the reviewed evidence.
No formalization of this result is known.