On Automorphisms of Arithmetic Subgroups of Unipotent Groups in Positive Characteristic
نویسنده
چکیده
1.1. Definition. It is traditional to say that a group Γ virtually has a property if some finite-index subgroup of Γ has the property. It is convenient to extend this terminology to group isomorphisms. • A virtual isomorphism from G1 to G2 is an isomorphism Λ: G ′ 1 → G ′ 2, where G ′ i is a finite-index, open subgroup of Gi. • A virtual automorphism of G is a virtual isomorphism from G to G. • A virtual isomorphism Λ from G1 to G2 virtually extends an isomorphism λ from Γ1 to Γ2 if there is a finite-index, open subgroup Γ ′ 1 of Γ1, such that Γ ′ 1 ⊂ G1, and Λ|Γ′ 1 = λ|Γ′ 1 .
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