  The bracket operation on mutually local BRST classes may be combined with
Lorentz invariance and analyticity to write an infinite set of finite
difference relations on string scattering amplitudes. When combined with some
simple physical criteria these relations uniquely determine the genus zero
string $S$-matrix for $N\leq 26$-particle scattering in $\IR^{25,1}$ in terms
of a single parameter, $\kappa$, the string coupling. We propose that the
high-energy limit of the relations are the Ward identities for the high-energy
symmetries of string theory.
