منابع مشابه
Measurable Perfect Matchings for Acyclic Locally Countable Borel graphs
We characterize the structural impediments to the existence of Borel perfect matchings for acyclic locally countable Borel graphs admitting a Borel selection of finitely many ends from their connected components. In particular, this yields the existence of Borel matchings for such graphs of degree at least three. As a corollary, it follows that acyclic locally countable Borel graphs of degree a...
متن کاملWhen Is the Semigroup Ring Perfect?
A characterization of perfect semigroup rings A[G] is given by means of the properties of the ring A and the semigroup G. It was proved in [10] that for a ring with unity A and a group G the group ring A[G] is perfect if and only if A is perfect and G is finite. Some results on perfectness of semigroup rings were obtained by Domanov [3]. He reduced the problem of describing perfect semigroup ri...
متن کاملOn Higher Dimensional Perfect Factors
A d-dimensional Perfect Factor is a collection of periodic arrays in which every k-ary (n1×· · ·×nd) matrix appears appears exactly once (periodically). The one dimensional case, with a collection of size one, is known as a De Bruijn cycle. The 1and 2-dimensional versions have proven highly applicable in areas such as coding, communications, and location sensing. Here we focus on results in hig...
متن کاملInfinite dimensional perfect set theorems
What largeness and structural assumptions on A ⊆ [R]ω can guarantee the existence of a non-empty perfect set P ⊆ R such that [P ]ω ⊆ A? Such a set P is called A-homogeneous. We show that even if A is open, in general it is independent of ZFC whether for a cardinal κ, the existence of an A-homogeneous set H ∈ [R]κ implies the existence of a non-empty perfect A-homogeneous set. On the other hand,...
متن کاملIrreducible representations of metrizable spaces and strongly countable-dimensional spaces
We generalize Freudenthal’s theory of irreducible representations of metrizable compacta by inverse sequences of compact polyhedra to the class of all metrizable spaces. Our representations consist of inverse sequences of completely metrizable polyhedra which are ANR’s. They are extendable: any such representation of a closed subspace of a given metrizable space extends to another such of the e...
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ژورنال
عنوان ژورنال: International Journal of Algebra
سال: 2014
ISSN: 1314-7595
DOI: 10.12988/ija.2014.3877