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Dense subgroups of finite groups

Published online by Cambridge University Press:  09 April 2009

Terence M. Gagen
Affiliation:
University of Sydney, Sydney, Australia
Paul M. Weichsel
Affiliation:
University of Illinois, Urbana, Illinois, U.S.A.
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It is well known that in the category of all groups and homomorphisms, every epimorphism is onto. This result does not hold for certain other categories of groups. The condition that an epimorphism θ:GA is not onto is equivalent to the condition that θ(G) is a proper subgroup A with the property that any two homomorphisms α, β on A which agree elementwise on θ(G) must agree on A. Such a subgroup can be called dense (see e.g. [1]). Naturally the existence of such homomorphisms α and β depend on the particular class of groups that is available. We will choose to work within the context of varieties even though many of the results will hold true for more modest classes of groups.

Type
Research Article
Copyright
Copyright © Australian Mathematical Society 1972

References

[1]Neumann, P. M., ‘Splitting groups and projectives in varieties of groups’, Quart. J. of Math. (Oxford Ser.) 18 (1967), 325332.CrossRefGoogle Scholar
[2]Hanna, Neumann, Varieties of Groups (Ergebnisse der Mathematik und ihrer Grenzgebiete, Band 37, Springer-Verlag, Berlin, 1967).Google Scholar
[3]Kovécs, L. G. and Newman, M. F., ‘Minimal verbal subgroups’, Proc. Cambridge Philos. Soc. 62 (1966), 347350.CrossRefGoogle Scholar