منابع مشابه
Quasi-projective covers of right $S$-acts
In this paper $S$ is a monoid with a left zero and $A_S$ (or $A$) is a unitary right $S$-act. It is shown that a monoid $S$ is right perfect (semiperfect) if and only if every (finitely generated) strongly flat right $S$-act is quasi-projective. Also it is shown that if every right $S$-act has a unique zero element, then the existence of a quasi-projective cover for each right act implies that ...
متن کاملquasi-projective covers of right $s$-acts
in this paper $s$ is a monoid with a left zero and $a_s$ (or $a$) is a unitary right $s$-act. it is shown that a monoid $s$ is right perfect (semiperfect) if and only if every (finitely generated) strongly flat right $s$-act is quasi-projective. also it is shown that if every right $s$-act has a unique zero element, then the existence of a quasi-projective cover for each right act implies that ...
متن کاملOrbifold Groups, Quasi-projectivity and Covers
We discuss properties of complex algebraic orbifold groups, their characteristic varieties, and their abelian covers. In particular, we deal with the question of (quasi)-projectivity of orbifold groups. We also prove a structure theorem for the variety of characters of normalcrossing quasi-projective orbifold groups. Finally, we extend Sakuma’s formula for the first Betti number of abelian cove...
متن کاملON QUASI UNIVERSAL COVERS FOR GROUPS ACTING ON TREES WITH INVERSIONS
Abstract. In this paper we show that if G is a group acting on a tree X with inversions and if (T Y ) is a fundamental domain for the action of G on X, then there exist a group &tildeG and a tree &tildeX induced by (T Y ) such that &tildeG acts on &tildeX with inversions, G is isomorphic to &tilde G, and X is isomorphic to &tildeX. The pair (&tilde G &tildeX) is called the quasi universal cover...
متن کاملCounting functions for branched covers of elliptic curves and quasi-modular forms
of the branched covers of an elliptic curve. Here, N (m) g,d is the (weighted) number of isomorphism classes of branched covers, with genus g(> 1), degree d, and ramification index (m,m, . . . ,m), of an elliptic curve. Such a cover is called an m-simple cover. Our aim is to prove that the formal power series F (m) g converges to a function belonging to the graded ring of quasi-modular forms wi...
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ژورنال
عنوان ژورنال: Bulletin of the Australian Mathematical Society
سال: 1986
ISSN: 0004-9727,1755-1633
DOI: 10.1017/s000497270000397x