@article{macfadyen:1971:cse,
    author = {Macfadyen, N. W. and Winternitz, P.},
     title = {Crossing symmetric expansions of physical scattering
              amplitudes: The $O(2,1)$ group and {L}am\'e functions},
   journal = {J. Mathematical Phys.},
    volume = {12},
      year = {1971},
     pages = {281–293},
   mrclass = {81.22},
  mrnumber = {MR0273921 (42 \#8797)},
       doi = {10.1063/1.1665589}}