  Denote the virtual cohomological dimension of SL_n(Z) by t=n(n-1)/2. Let St
denote the Steinberg module of SL_n(Q) tensored with Q. Let Sh_* denote the
sharbly resolution of the Steinberg module St. By Borel-Serre duality, the
one-dimensional Q-vector space H^0(SL_n(Z), Q) is isomorphic to
H_t(SL_n(Z),St). We find an explicit generator of H_t(SL_n(Z),St) in terms of
sharbly cycles and cosharbly cocycles. These methods may extend to other
degrees of cohomology of SL_n(Z).
