Extensible automorphism

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extensible equals inner: A proof that every extensible automorphism of a group is an inner automorphism. An automorphism $σ$ of a group $G$ is termed extensible if for any group $H$ containing $G$ , there exists an automorphism $σ'$ of $H$ whose restriction to $G$ equals $σ$ .
extensible automorphisms problem: A discussion of extensibility of automorphisms and related questions.
group property-conditionally extensible automorphism: The property of an automorphism being extensible with respect to a group property.
variety-extensible automorphism: extensibility with respect to a variety of algebras.