  We consider the dependence of the entropic solution of a hyperbolic system of
conservation laws \[ \{\{array}{c} u_t + f(u)_x = 0 u(0,\cdot) = u_0 \{array}
\] on the flux function f. We prove that the solution in Lipschitz continuous
w.r.t.~the $C^0$ norm of the derivative of the perturbation of f. We apply this
result to prove the convergence of the solution of the relativistic Euler
equation to the classical limit.
