We consider a hyperbolic system of conservation laws where each characteristic field is either linearly degenerate or genuinely nonlinear. Under the assumption of coinciding shock and rarefaction curves and the existence of a set of Riemann coordinates w, w prove that there exists a semigroup of solutions u(t) = S(t)u(0), defined on initial data u(0) is an element of L-infinity. The semigroup S is continuous w.r.t. time and the initial data u(0) in the L-loc(1) topology. Moreover, S is unique and its trajectories are obtained as limits of wave front tracking approximations
