  For n > 2, the Dehn functions of Aut(F_n) and Out(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>4 to the case n=3. In this note we give a shorter, more direct proof of this
last reduction.

Group Theory;Geometric Topology