  We consider the problem of supersonic flow of a Chaplygin gas past a delta
wing with a shock or rarefaction wave attached to the leading edges. The flow
under study is described by the three-dimensional steady Euler system. In
conical coordinates, this problem can be reformulated as a boundary value
problem for a nonlinear equation of mixed type. The type of this equation
depends fully on the solutions of the problem itself, and thus it cannot be
determined in advance. We overcome the difficulty by establishing a crucial
Lipschitz estimate, and finally prove the unique existence of the solution via
the method of continuity.
