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Co-rank and Betti number of a group

Irina Gelbukh (2015)

Czechoslovak Mathematical Journal

For a finitely generated group, we study the relations between its rank, the maximal rank of its free quotient, called co-rank (inner rank, cut number), and the maximal rank of its free abelian quotient, called the Betti number. We show that any combination of the group's rank, co-rank, and Betti number within obvious constraints is realized for some finitely presented group (for Betti number equal to rank, the group can be chosen torsion-free). In addition, we show that the Betti number is additive...

Groups whose proper subgroups are locally finite-by-nilpotent

Amel Dilmi (2007)

Annales mathématiques Blaise Pascal

If 𝒳 is a class of groups, then a group G is said to be minimal non 𝒳 -group if all its proper subgroups are in the class 𝒳 , but G itself is not an 𝒳 -group. The main result of this note is that if c > 0 is an integer and if G is a minimal non ( ℒℱ ) 𝒩 (respectively, ( ℒℱ ) 𝒩 c )-group, then G is a finitely generated perfect group which has no non-trivial finite factor and such that G / F r a t ( G ) is an infinite simple group; where 𝒩 (respectively, 𝒩 c , ℒℱ ) denotes the class of nilpotent (respectively, nilpotent of class at most c , locally...

Homology theory in the alternative set theory I. Algebraic preliminaries

Jaroslav Guričan (1991)

Commentationes Mathematicae Universitatis Carolinae

The notion of free group is defined, a relatively wide collection of groups which enable infinite set summation (called commutative π -group), is introduced. Commutative π -groups are studied from the set-theoretical point of view and from the point of view of free groups. Commutativity of the operator which is a special kind of inverse limit and factorization, is proved. Tensor product is defined, commutativity of direct product (also a free group construction and tensor product) with the special...

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