We consider the c = 1 matrix model deformed by the operator 2M TrÎ¦ âˆ’2, which was conjectured by Jevicki and Yoneya to describe a two-dimensional black hole of mass M . We calculate the exact non-perturbative S-matrix and show that all the amplitudes involving an odd number of particles vanish at least to all orders of perturbation theory. We conjecture thatâ€¦ (More)