Automorphism groups

The automorphism group as an object: orders of automorphism groups, realizing groups as (outer) automorphism groups, class-preserving and inner automorphisms, automorphism orbits, endomorphism counts.

DefinitionGroups with finitely many automorphism orbits#✓fully proved

A group \(G\) has finitely many automorphism orbits if the action of its automorphism group \(\operatorname{Aut}(G)\) on \(G\) has only finitely many orbits.

def HasFinitelyManyAutomorphismOrbits (G : Type*) [Group G] : Prop :=
  Finite (MulAction.orbitRel.Quotient (MulAut G) G)

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