Jonathan Schilhan

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2ranked-venue papers
2as first author
2since 2021 · last 2026
0000-0001-6696-1603ORCID · corroborated

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Theory of computation · 2 · 2 first-author · 2 since 2021
YearPublicationVenuePosition
2026 Maximal sets without choice
abstract
We show that it is consistent relative to ZF , that there is no well-ordering of R while a wide class of special sets of reals such as Hamel bases, transcendence bases, Vitali sets or Bernstein sets exists. To be more precise, we can assume that every projective hypergraph on R has a maximal independent set, among a few other things. For example, we get transversals for all projective equivalence relations. Moreover, this is possible while either DC ω 1 holds, or countable choice for reals fails. Assuming the consistency of an inaccessible cardinal, “projective” can even be replaced with “ L ( R ) ” and we can add that any instance of AC in L ( R ) has a choice function. This vastly strengthens the consistency results obtained in [6] , [11] or [15] .
Jonathan Schilhan
Ann. Pure Appl. Log.1
2022 Tree Forcing and Definable Maximal Independent Sets in Hypergraphs
abstract
Abstract We show that after forcing with a countable support iteration or a finite product of Sacks or splitting forcing over L, every analytic hypergraph on a Polish space admits a $\mathbf {\Delta }^1_2$ maximal independent set. This extends an earlier result by Schrittesser (see [25]). As a main application we get the consistency of $\mathfrak {r} = \mathfrak {u} = \mathfrak {i} = \omega _2$ together with the existence of a $\Delta ^1_2$ ultrafilter, a $\Pi ^1_1$ maximal independent family, and a $\Delta ^1_2$ Hamel basis. This solves open problems of Brendle, Fischer, and Khomskii [5] and the author [23]. We also show in ZFC that $\mathfrak {d} \leq \mathfrak {i}_{cl}$ , addressing another question from [5].
Jonathan Schilhan
J. Symb. Log.1