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Wall's obstructions and Whitehead torsion.

Slawomir Kwasik (1983)

Commentarii mathematici Helvetici

Weak Adjoint Functors.

Paul C. Kainen (1971)

Mathematische Zeitschrift

Weak alg-universality and $Q$ -universality of semigroup quasivarieties

Marie Demlová, Václav Koubek (2005)

Commentationes Mathematicae Universitatis Carolinae

In an earlier paper, the authors showed that standard semigroups $𝐌_{1}$ , $𝐌_{2}$ and $𝐌_{3}$ play an important role in the classification of weaker versions of alg-universality of semigroup varieties. This paper shows that quasivarieties generated by $𝐌_{2}$ and $𝐌_{3}$ are neither relatively alg-universal nor $Q$ -universal, while there do exist finite semigroups $𝐒_{2}$ and $𝐒_{3}$ generating the same semigroup variety as $𝐌_{2}$ and $𝐌_{3}$ respectively and the quasivarieties generated by $𝐒_{2}$ and/or $𝐒_{3}$ are quasivar-relatively $f f$ -alg-universal and $Q$ -universal...

Weak Baer modules over graded rings

Mark Teply, Blas Torrecillas (1998)

Colloquium Mathematicae

In [2], Fuchs and Viljoen introduced and classified the $B^{*}$ -modules for a valuation ring R: an R-module M is a $B^{*}$ -module if $E x t_{R}^{1} (M, X) = 0$ for each divisible module X and each torsion module X with bounded order. The concept of a $B^{*}$ -module was extended to the setting of a torsion theory over an associative ring in [14]. In the present paper, we use categorical methods to investigate the $B^{*}$ -modules for a group graded ring. Our most complete result (Theorem 4.10) characterizes $B^{*}$ -modules for a strongly graded ring R...