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On a class of commutative groupoids determined by their associativity triples

Aleš Drápal (1993)

Commentationes Mathematicae Universitatis Carolinae

Let G = G ( · ) be a commutative groupoid such that { ( a , b , c ) G 3 ; a · b c a b · c } = { ( a , b , c ) G 3 ; a = b c or a b = c } . Then G is determined uniquely up to isomorphism and if it is finite, then card ( G ) = 2 i for an integer i 0 .

On a class of finite solvable groups

James Beidleman, Hermann Heineken, Jack Schmidt (2013)

Open Mathematics

A finite solvable group G is called an X-group if the subnormal subgroups of G permute with all the system normalizers of G. It is our purpose here to determine some of the properties of X-groups. Subgroups and quotient groups of X-groups are X-groups. Let M and N be normal subgroups of a group G of relatively prime order. If G/M and G/N are X-groups, then G is also an X-group. Let the nilpotent residual L of G be abelian. Then G is an X-group if and only if G acts by conjugation on L as a group...

On a class of locally Butler groups

Ladislav Bican (1991)

Commentationes Mathematicae Universitatis Carolinae

A torsionfree abelian group B is called a Butler group if B e x t ( B , T ) = 0 for any torsion group T . It has been shown in [DHR] that under C H any countable pure subgroup of a Butler group of cardinality not exceeding ω is again Butler. The purpose of this note is to show that this property has any Butler group which can be expressed as a smooth union α < μ B α of pure subgroups B α having countable typesets.

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