**Keywords:**

In this paper we describe certain crucial steps for developing an algorithm to find the Riemann solution in systems of conservation laws in which the Lax hypotheses of strict hyperbolicity and genuine nonlinearity are relaxed. First, we present a procedure for continuing wave curves beyond points where characteristic speeds coincide. This procedure requires strict hyperbolicity on both sides of the coincidence locus. Loss of strict hyperbolicity is regularized by means of a generalized Jordan chain, which serves to construct a four-fold submanifold structure on which wave curves can be continued. Second, we analyze the case of loss of genuine nonlinearity. We prove a new result: the existence of composite wave curves when the composite wave traverses either the inflection locus or an anomalous part of the non-local composite wave curve. In this sense, we find conditions under which the composite field is well defined and its singularities can be removed, allowing use of our continuation method. Finally, we present numerical examples for a non-strictly hyperbolic system of conservation laws.

**MSC 2000:**65M06

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