Towards the theory of integrable hyperbolic equations of third order
  The examples are considered of integrable hyperbolic equations of third order with two independent variables. In particular, an equation is found which admits as evolutionary symmetries the Krichever--Novikov equation and the modified Landau--Lifshitz system. The problem of choice of dynamical variables for the hyperbolic equations is discussed. 
V. E. Adler, A. B. Shabat
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