What is a double central extension? (The question was asked by Ronald Brown). (English) Zbl 0762.18003

The author obtains an answer to this question for groups by applying his Galois theory in general categories to a particular category: the arrow category of the category of groups.


18A99 General theory of categories and functors
20J15 Category of groups
18B99 Special categories
Full Text: Numdam EuDML


[1] 1 R. Brown & G.J. Ellis , ’Hopf formulae for the higher homology of a group’ , Bull. London Math. Soc. 20 ( 1988 ) 124 - 128 . MR 924238 | Zbl 0611.20032 · Zbl 0611.20032
[2] 2 G. Janalidze , ’Pure Galois theory in categories’ , J. Algebra 132 ( 1990 ) 270 - 286 . (First version was available as UCNW Preprint 87.20, Bangor , 1987 .) MR 1061480
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