  A dual formulation of the S Matrix for N=4 SYM has recently been presented,
where all leading singularities of n-particle N^{k-2}MHV amplitudes are given
as an integral over the Grassmannian G(k,n), with cyclic symmetry, parity and
superconformal invariance manifest. In this short note we show that the dual
superconformal invariance of this object is also manifest. The geometry
naturally suggests a partial integration and simple change of variable to an
integral over G(k-2,n). This change of variable precisely corresponds to the
mapping between usual momentum variables and the "momentum twistors" introduced
by Hodges, and yields an elementary derivation of the momentum-twistor space
formula very recently presented by Mason and Skinner, which is manifestly dual
superconformal invariant. Thus the G(k,n) Grassmannian formulation allows a
direct understanding of all the important symmetries of N=4 SYM scattering
amplitudes.
