The Dehn functions of Out(Fn) and Aut(Fn)

Abstract

For n at least 3, the Dehn functions of Out(Fn) and Aut(F n) are exponential. Hatcher and Vogtmann proved that they are at most exponential, and the complementary lower bound in the case n = 3 was established by Bridson and Vogtmann. Handel and Mosher completed the proof by reducing the lower bound for n bigger than 3 to the case n = 3. In this note we give a shorter, more direct proof of this last reduction. © Association des Annales de l'institut Fourier, 2012, tous droits réservés.