“…Solution semigroups that are Lipschitz in L 1 but not contractive may exist and are of physical interest (see [54]), but their study will not be addressed in the present paper. A comparable theory for conservation laws with discontinuous flux is still not available, although these equations have received intense attention in last fifteen years; see [1,2,3,12,13,14,19,20,21,23,26,29,30,31,32,35,37,38,42,43,44,45,46,47,48,49,59,60,62,69,70,73,76,77] (and additional references therein) for a number of different admissibility criteria, existence and/or uniqueness results, which we partially revisit in Section 4. Recently, it was pointed out explicitly by Adimurthi, Mishra, and Veerappa Gowda in [3] that for the case f = f(x, u) with f piecewise constant in x, there may exist many different L 1 -contractive semigroups of solutions to (1.1).…”