@article{ludwig:1966:uae,
    author = {Ludwig, Donald},
     title = {Uniform asymptotic expansions at a caustic},
   journal = {Comm. Pure Appl. Math.},
    volume = {19},
      year = {1966},
     pages = {215–250},
   mrclass = {35.75},
  mrnumber = {MR0196254 (33 \#4446)},
mrreviewer = {Colin Clark},
       doi = {10.1002/cpa.3160190207},
     zblno = {0163.13703}}