A presentation for the special automorphism group of a free group

A presentation is given for SA_n, the group of automorphisms of determinant 1 of a free group F_n of rank n. The canonical isomorphisms $\text{H}{}_2\text{(A}{}_{\mathrm{n}}\text{,}\text{Z}\text{)}\text{?}\text{H}{}_2\text{(SA}{}_{\mathrm{n}}\text{,}\text{Z}\text{)}\text{?}\text{K}{}_2\text{(}\text{Z}\text{)}$ are established for n ≥ 5, where A_n is the full group of automorphisms of F_n.