Peter D. Lax 
Hyperbolic Systems of Conservation Laws in Several Space Variables [PDF ebook] 

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. In Section 1 we show how to associate to each analytic function f of one variable a complex conservation law. When written in terms of real variables, this equation turns into a symmetric hyperbolic system of two first order conservation laws in time and two space variables for two unknowns. The’ hope is that the theory of analytic functions can be exploited to study the properties of the solutions of these model equations.