Date: Mar 24, 2013 7:26 PM
Author: Jose Carlos Santos
Subject: Re: name for definition in group theory
On 24/03/2013 22:35, Arturo Magidin wrote:

>>> Since G is abelian, the map x -> -x is an automorphism.

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>>> Since this must be trivial, we have x + x = 0 for all

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>>> x. Hence G is a vector space over Z_2. And now as

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>>> above, if dim(G) = 0 or 1 then |G| = 1 or 2, while

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>>> if dim(G) > 1 then G has a non-trivial automorphism.

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>> Is this necessarily true without the axiom of choice?

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> No, it is not necessarily true without the Axiom of Choice. Without AC, one can construct a vector space over GF(2) that is nontrivial but has trivial automorphism group. See

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> http://math.stackexchange.com/questions/28145/axiom-of-choice-and-automorphisms-of-vector-spaces/29469#29469

Thanks!

Best regards,

Jose Carlos Santos