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- Sy-David Friedman, Ralf Schindler
- J. Symb. Log.
- 2003

Let n ≥ 3 be an integer. We show that it is consistent (relative to the consistency of n − 2 strong cardinals) that every Σn-set of reals is universally Baire yet there is a (lightface) projective well-ordering of the reals. The proof uses ”David’s trick” in the presence of inner models with strong cardinals.

- Sy-David Friedman, Menachem Magidor
- J. Symb. Log.
- 2009

There have been numerous results showing that a measurable cardinal κ can carry exactly α normal measures in a model of GCH, where α is a cardinal at most κ++. Starting with just one measurable cardinal, we have [9] (for α = 1), [10] (for α = κ++, the maximum possible) and [1] (for α = κ+, after collapsing κ++). In addition, under stronger large cardinal… (More)

- Sy-David Friedman, Radek Honzik, Lyubomyr Zdomskyy
- Ann. Pure Appl. Logic
- 2013

In this paper we introduce some fusion properties of forcing notions which guarantee that an iteration with supports of size ≤ κ not only does not collapse κ but also preserves the strength of κ (after a suitable preparatory forcing). This provides a general theory covering the known cases of tree iterations which preserve large cardinals (cf. [4, 5, 6, 8,… (More)

- David Asperó, Sy-David Friedman
- Ann. Pure Appl. Logic
- 2009

By forcing over amodel of ZFC+ GCH (aboveא0) with a class-sized partial order preserving this theory we produce a model in which there is a locally defined well-order of the universe; that is, one whose restriction to all levels H(κ) (κ ≥ ω2 a regular cardinal) is a well-order of H(κ) definable over the structure 〈H(κ),∈〉 by a parameter-free formula.… (More)

- Natasha Dobrinen, Sy-David Friedman
- Arch. Math. Log.
- 2008

- Tatiana Arrigoni, Sy-David Friedman
- Bulletin of Symbolic Logic
- 2013

- Ekaterina B. Fokina, Sy-David Friedman, Asger Törnquist
- Ann. Pure Appl. Logic
- 2010

The study of Borel equivalence relations under Borel reducibility has developed into an important area of descriptive set theory. The dichotomies of Silver ([19]) and Harrington-Kechris-Louveau ([5]) show that with respect to Borel reducibility, any Borel equivalence relation strictly above equality on ω is above equality on P(ω), the power set of ω, and… (More)

- Ekaterina B. Fokina, Sy-David Friedman
- Math. Log. Q.
- 2012

We study the structure of Σ1 equivalence relations on hyperarithmetical subsets of ω under reducibilities given by hyperarithmetical or computable functions, called h-reducibility and FF-reducibility, respectively. We show that the structure is rich even when one fixes the number of properly Σ1 (i.e. Σ 1 1 but not ∆ 1 1) equivalence classes. We also show… (More)

- Sy-David Friedman, Radek Honzik
- Ann. Pure Appl. Logic
- 2008

The continuum function F on regular cardinals is known to have great freedom; if α, β are regular cardinals, then F needs only obey the following two restrictions: (1) cf(F (α)) > α, (2) α < β → F (α) ≤ F (β). However, if we wish to preserve measurable cardinals in the generic extension, new restrictions must be put on F . We say that κ is F… (More)

We study the complexity of the isomorphism relation on classes of computable structures. We use the notion of FF -reducibility introduced in [9] to show completeness of the isomorphism relation on many familiar classes in the context of all Σ1 equivalence relations on hyperarithmetical subsets of ω.