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Clones on regular cardinals

Martin Goldstern, Saharon Shelah (2002)

Fundamenta Mathematicae

We investigate the structure of the lattice of clones on an infinite set X. We first observe that ultrafilters naturally induce clones; this yields a simple proof of Rosenberg’s theorem: there are 2 2 λ maximal (= “precomplete”) clones on a set of size λ. The clones we construct do not contain all unary functions. We then investigate clones that do contain all unary functions. Using a strong negative partition theorem from pcf theory we show that for cardinals λ (in particular, for all successors of...

Clopen graphs

Stefan Geschke (2013)

Fundamenta Mathematicae

A graph G on a topological space X as its set of vertices is clopen if the edge relation of G is a clopen subset of X² without the diagonal. We study clopen graphs on Polish spaces in terms of their finite induced subgraphs and obtain information about their cochromatic numbers. In this context we investigate modular profinite graphs, a class of graphs obtained from finite graphs by taking inverse limits. This continues the investigation of continuous colorings on Polish spaces and their homogeneity...

Closed discrete subsets of separable spaces and relative versions of normality, countable paracompactness and property ( a )

Samuel Gomes da Silva (2011)

Commentationes Mathematicae Universitatis Carolinae

In this paper we show that a separable space cannot include closed discrete subsets which have the cardinality of the continuum and satisfy relative versions of any of the following topological properties: normality, countable paracompactness and property ( a ) . It follows that it is consistent that closed discrete subsets of a separable space X which are also relatively normal (relatively countably paracompact, relatively ( a ) ) in X are necessarily countable. There are, however, consistent examples of...

Club-guessing and non-structure of trees

Tapani Hyttinen (2001)

Fundamenta Mathematicae

We study the possibilities of constructing, in ZFC without any additional assumptions, strongly equivalent non-isomorphic trees of regular power. For example, we show that there are non-isomorphic trees of power ω₂ and of height ω · ω such that for all α < ω₁· ω · ω, E has a winning strategy in the Ehrenfeucht-Fraïssé game of length α. The main tool is the notion of a club-guessing sequence.

Club-guessing, good points and diamond

Pierre Matet (2007)

Commentationes Mathematicae Universitatis Carolinae

Shelah’s club-guessing and good points are used to show that the two-cardinal diamond principle ◊ κ , λ holds for various values of κ and λ .

Coalgebras for binary methods : properties of bisimulations and invariants

Hendrik Tews (2001)

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications

Coalgebras for endofunctors 𝒞 → 𝒞 can be used to model classes of object-oriented languages. However, binary methods do not fit directly into this approach. This paper proposes an extension of the coalgebraic framework, namely the use of extended polynomial functors 𝒞 o p × 𝒞 → 𝒞 . This extension allows the incorporation of binary methods into coalgebraic class specifications. The paper also discusses how to define bisimulation and invariants for coalgebras of extended polynomial functors and proves many standard...

Coalgebras for Binary Methods: Properties of Bisimulations and Invariants

Hendrik Tews (2010)

RAIRO - Theoretical Informatics and Applications

Coalgebras for endofunctors 𝒞 → 𝒞 can be used to model classes of object-oriented languages. However, binary methods do not fit directly into this approach. This paper proposes an extension of the coalgebraic framework, namely the use of extended polynomial functors 𝒞 o p × 𝒞 → 𝒞 . This extension allows the incorporation of binary methods into coalgebraic class specifications. The paper also discusses how to define bisimulation and invariants for coalgebras of extended polynomial functors and proves many...

Coalitional fuzzy preferences

Milan Mareš (2002)

Kybernetika

The paper deals with the concept of coalitional preferences in the group decision-making situations in which the agents and coalitions have only vague idea about the comparative acceptability of particular outcomes. The coalitional games with vague utilities (see, e. g., [6]) can serve for a good example when some types of the game solutions (e. g., the von Neumann– Morgenstern one) are to be extended to the fuzzy game case. In this paper, we consider the fuzzy analogies of coalitional preferences...

Cofinal types of topological directed orders

SŁawomir Solecki, Stevo Todorcevic (2004)

Annales de l’institut Fourier

We investigate the structure of the Tukey ordering among directed orders arising naturally in topology and measure theory.

Cohen real and disjoint refinement of perfect sets

Miroslav Repický (2000)

Commentationes Mathematicae Universitatis Carolinae

We prove that if there exists a Cohen real over a model, then the family of perfect sets coded in the model has a disjoint refinement by perfect sets.

Coherent adequate sets and forcing square

John Krueger (2014)

Fundamenta Mathematicae

We introduce the idea of a coherent adequate set of models, which can be used as side conditions in forcing. As an application we define a forcing poset which adds a square sequence on ω₂ using finite conditions.

Colimit-dense subcategories

Jiří Adámek, Andrew D. Brooke-Taylor, Tim Campion, Leonid Positselski, Jiří Rosický (2019)

Commentationes Mathematicae Universitatis Carolinae

Among cocomplete categories, the locally presentable ones can be defined as those with a strong generator consisting of presentable objects. Assuming Vopěnka’s Principle, we prove that a cocomplete category is locally presentable if and only if it has a colimit dense subcategory and a generator consisting of presentable objects. We further show that a 3 -element set is colimit-dense in 𝐒𝐞𝐭 op , and spaces of countable dimension are colimit-dense in 𝐕𝐞𝐜 op .

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