Complexity of curves
We show that each of the classes of hereditarily locally connected, finitely Suslinian, and Suslinian continua is Π₁¹-complete, while the class of regular continua is Π₀⁴-complete.
Complexity of the axioms of the alternative set theory
If T is a complete theory stronger than ZF such that axiom of extensionality for classes + T + is consistent for 1 (each alone), where are normal formulae then we show AST + + scheme of choice is consistent. As a consequence we get: there is no proper -formula in AST + scheme of choice. Moreover the complexity of the axioms of AST is studied, e.gẇe show axiom of extensionality is -formula, but not -formula and furthermore prolongation axiom, axioms of choice and cardinalities are -formulae,...
Complexity of the class of Peano functions
We evaluate the descriptive set theoretic complexity of the space of continuous surjections from to .
Complexity of the decidability of the unquantified set theory with a rank operator.
Composition of axial functions of products of finite sets
We show that every function f: A × B → A × B, where |A| ≤ 3 and |B| < ω, can be represented as a composition f₁ ∘ f₂ ∘ f₃ ∘ f₄ of four axial functions, where f₁ is a vertical function. We also prove that for every finite set A of cardinality at least 3, there exist a finite set B and a function f: A × B → A × B such that f ≠ f₁ ∘ f₂ ∘ f₃ ∘ f₄ for any axial functions f₁, f₂, f₃, f₄, whenever f₁ is a horizontal function.
Composition of shape generators
Compositions of ternary relations
In this paper, we introduce six basic types of composition of ternary relations, four of which are associative. These compositions are based on two types of composition of a ternary relation with a binary relation recently introduced by Zedam et al. We study the properties of these compositions, in particular the link with the usual composition of binary relations through the use of the operations of projection and cylindrical extension.
Computability in special models.
Concept lattices associated with L-fuzzy W-contexts.
Condensation and large cardinals
We introduce two generalized condensation principles: Local Club Condensation and Stationary Condensation. We show that while Strong Condensation (a generalized condensation principle introduced by Hugh Woodin) is inconsistent with an ω₁-Erdős cardinal, Stationary Condensation and Local Club Condensation (which should be thought of as weakenings of Strong Condensation) are both consistent with ω-superstrong cardinals.
Conjugacy equivalence relation on subgroups
If G is a countable group containing a copy of F₂ then the conjugacy equivalence relation on subgroups of G attains the maximal possible complexity.
Connections between different amoeba algebras
Connectivity properties of sequential Boolean algebras
Consistency of the Silver dichotomy in generalised Baire space
Silver’s fundamental dichotomy in the classical theory of Borel reducibility states that any Borel (or even co-analytic) equivalence relation with uncountably many classes has a perfect set of classes. The natural generalisation of this to the generalised Baire space for a regular uncountable κ fails in Gödel’s L, even for κ-Borel equivalence relations. We show here that Silver’s dichotomy for κ-Borel equivalence relations in for uncountable regular κ is however consistent (with GCH), assuming...
Consistency property and model existence theorem for second order negative languages with conjunctions and quantifications over sets of cardinality smaller than a strong limit cardinal of denumerable cofinality
Consistency statements in formal theories
Constructibility and shiftings of view
Constructibility in Ackermann's set theory [Book]
Constructing a maximal cofinitary group.
Constructing universally small subsets of a given packing index in Polish groups
A subset of a Polish space X is called universally small if it belongs to each ccc σ-ideal with Borel base on X. Under CH in each uncountable Abelian Polish group G we construct a universally small subset A₀ ⊂ G such that |A₀ ∩ gA₀| = for each g ∈ G. For each cardinal number κ ∈ [5,⁺] the set A₀ contains a universally small subset A of G with sharp packing index equal to κ.