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Moduli of graphs and automorphisms of free groups. (English) Zbl 0589.20022
From the author’s introduction: ”This paper represents the beginning of an attempt to transfer, to the study of outer automorphisms of free groups, the powerful geometric techniques that were invented by Thurston to study mapping classes of surfaces. Let \(F_ n\) denote the free group of rank n. We will study the group \(Out(F_ n)\) of outer automorphisms of \(F_ n\) by studying its action on a space \(X_ n\) which is analogous to the Teichm├╝ller space of hyperbolic metrics on a surface; the points of \(X_ n\) are metric structures on graphs with fundamental group \(F_ n.''\) The main result of this paper is that the space \(X_ n\) is contractible. This has as a corollary that the group \(Out(F_ n)\) has virtual cohomological dimension 2n-3.
Reviewer: S.Andreadakis

20F28 Automorphism groups of groups
20E05 Free nonabelian groups
20F34 Fundamental groups and their automorphisms (group-theoretic aspects)
20J05 Homological methods in group theory
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