CONTACT GEOMETRY OF SECOND ORDER I KEIZO YAMAGUCHI

In [C1] and [C2], E.Cartan studied involutive systems of second order partial differential equations for a scalar function with 2 or 3 independent variables, following the tradition of the geometric theory of partial differential equations developed by Monge, Jacobi, Lie, Darboux, Goursat and others. In fact he investigated the contact equivalence and th