Remarks on a paper of D. Ludwig

[1]  L. Hörmander.  Fourier integral operators. I , 1995 .

[2]  Donald Ludwig,et al.  Uniform asymptotic expansions at a caustic , 1966 .

[3]  C. Chester,et al.  An extension of the method of steepest descents , 1957, Mathematical Proceedings of the Cambridge Philosophical Society.

[4]  Harold Levine,et al.  Singularities of differentiable mappings , 1971 .