Closure operators and generating sets
Closure operators on radical classes of lattice-ordered groups
Closure operators on the lattice of radical classes of lattice ordered groups
Closure properties for relational systems with given endomorphism structure
Closure rings
We consider rings equipped with a closure operation defined in terms of a collection of commuting idempotents, generalising the idea of a topological closure operation defined on a ring of sets. We establish the basic properties of such rings, consider examples and construction methods, and then concentrate on rings which have a closure operation defined in terms of their lattice of central idempotents.
Coaxial filters of distributive lattices
Coaxial filters and strongly coaxial filters are introduced in distributive lattices and some characterization theorems of -lattices are given in terms of co-annihilators. Some properties of coaxial filters of distributive lattices are studied. The concept of normal prime filters is introduced and certain properties of coaxial filters are investigated. Some equivalent conditions are derived for the class of all strongly coaxial filters to become a sublattice of the filter lattice.
Cocompact lattices.
Cocycle condition for multi-pullbacks of algebras
Take finitely many topological spaces and for each pair of these spaces choose a pair of corresponding closed subspaces that are identified by a homeomorphism. We note that this gluing procedure does not guarantee that the building pieces, or the gluings of some pieces, are embedded in the space obtained by putting together all given ingredients. Dually, we show that a certain sufficient condition, called the cocycle condition, is also necessary to guarantee sheaf-like properties of surjective multi-pullbacks...
Coefficients d'accord entre deux préordres totaux
Coefficients d'accord entre deux préordres totaux. Comparaison ordinale des coefficients
Cofinal types of topological directed orders
We investigate the structure of the Tukey ordering among directed orders arising naturally in topology and measure theory.
Cofinalities of complete Boolean algebras.
Cofinalities of doubly transitive sets.
Coherent spaces constructively
Coherent ultrafilters and nonhomogeneity
We introduce the notion of a coherent -ultrafilter on a complete ccc Boolean algebra, strengthening the notion of a -point on , and show that these ultrafilters exist generically under . This improves the known existence result of Ketonen [On the existence of -points in the Stone-Čech compactification of integers, Fund. Math. 92 (1976), 91–94]. Similarly, the existence theorem of Canjar [On the generic existence of special ultrafilters, Proc. Amer. Math. Soc. 110 (1990), no. 1, 233–241] can...
Colimits of representable algebra-valued functors.
Collapsing along monotone poset maps.
Coloring digraphs by iterated antichains
We show that the minimum chromatic number of a product of two -chromatic graphs is either bounded by 9, or tends to infinity. The result is obtained by the study of coloring iterated adjoints of a digraph by iterated antichains of a poset.
Combinatoria e Topologia. Alcune considerazioni generali
Si descrive un metodo generale mediante il quale associare in modo naturale spazi topologici ad insiemi parzialmente ordinati e funzioni continue afunzioni monotone tra di essi; questa associazione è chiaramente la chiave di volta per fondare l’utilizzo di metodi topologici nella teoria combinatoria degli insiemi parzialmente ordinati. Si discutono quindi alcuni criteri di contraibilità e si presenta una breve introduzione alla teoria dei «poset Cohen-Macaulay». Il lavoro si conclude con una sezione...
Combinatorial construction of toric residues.
In this paper we investigate the problem of finding an explicit element whose toric residue is equal to one. Such an element is shown to exist if and only if the associated polytopes are essential. We reduce the problem to finding a collection of partitions of the lattice points in the polytopes satisfying a certain combinatorial property. We use this description to solve the problem when and for any when the polytopes of the divisors share a complete flag of faces. The latter generalizes earlier...