Outer automorphism group
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This article is about a basic definition in group theory. The article text may, however, contain advanced material.
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Definition
Let be a group. The outer automorphism group of
, denoted
, is defined as the quotient group of the automorphism group
by the inner automorphism group
.
Elements of the outer automorphism group are sometimes termed outer automorphism classes. Each outer automorphism class is a coset of the inner automorphism group -- it is not a single automorphism. Thus, the outer automorphism group is not the set of outer automorphisms.