منابع مشابه
Covers Induced by Ext
We prove a generalization of the Flat Cover Conjecture by showing for any ring R that (1) each (right R-) module has a Ker Ext(−, C)-cover, for any class of pure-injective modules C, and that (2) each module has a Ker Tor(−,B)-cover, for any class of left R-modules B. For Dedekind domains, we describe Ker Ext(−, C) explicitly for any class of cotorsion modules C; in particular, we prove that (1...
متن کاملExt Groups and Ext Functors
If A and B are Abelian groups, then Hom(A,B) is also an Abelian group under pointwise addition of functions. In this section we will see how Hom gives rise to classes of functors. Let A denote the category of Abelian groups. A covariant functor T : A → A associates to every Abelian group A an Abelian group T (A), and for every homomorphism f : A → B a homomorphism T (f) : T (A)→ T (B), such tha...
متن کاملInduced Graphoidal Covers in a Graph
An induced graphoidal cover of a graph G is a collection ψ of (not necessarily open) paths in G such that every path in ψ has at least two vertices, every vertex of G is an internal vertex of at most one path in ψ, every edge of G is in exactly one path in ψ and every member of ψ is an induced cycle or an induced path. The minimum cardinality of an induced graphoidal cover of G is called the in...
متن کاملInduced Acyclic Graphoidal Covers in a Graph
An induced acyclic graphoidal cover of a graph G is a collection ψ of open paths in G such that every path in ψ has atleast two vertices, every vertex of G is an internal vertex of at most one path in ψ, every edge of G is in exactly one path in ψ and every member of ψ is an induced path. The minimum cardinality of an induced acyclic graphoidal cover of G is called the induced acyclic graphoida...
متن کاملVertex covers by edge disjoint
Let H be a simple graph having no isolated vertices. An (H; k)-vertex-cover of a simple graph G = (V;E) is a collection H1; : : : ;Hr of subgraphs of G satisfying 1. Hi = H; for all i = 1; : : : ; r; 2. [i=1V (Hi) = V , 3. E(Hi) \ E(Hj) = ;; for all i 6= j; and 4. each v 2 V is in at most k of the Hi. We consider the existence of such vertex covers when H is a complete graph, Kt; t 3, in the co...
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ژورنال
عنوان ژورنال: Journal of Algebra
سال: 2000
ISSN: 0021-8693
DOI: 10.1006/jabr.2000.8343