The light in the neighborhood of a caustic
Séminaire Bourbaki : vol. 1976/77, exposés 489-506, Séminaire Bourbaki, no. 19 (1978), Exposé no. 490, 11 p. 
@incollection{SB_1976-1977__19__19_0,
     author = {Duistermaat, J. J.},
     title = {The light in the neighborhood of a caustic},
     booktitle = {S\'eminaire Bourbaki : vol. 1976/77, expos\'es 489-506},
     author = {Collectif},
     series = {S\'eminaire Bourbaki},
     note = {talk:490},
     publisher = {Springer-Verlag},
     number = {19},
     year = {1978},
     zbl = {0401.35063},
     mrnumber = {521757},
     language = {en},
     url = {archive.numdam.org/item/SB_1976-1977__19__19_0/}
}
Duistermaat, J. J. The light in the neighborhood of a caustic, dans Séminaire Bourbaki : vol. 1976/77, exposés 489-506, Séminaire Bourbaki, no. 19 (1978), Exposé no. 490, 11 p. http://archive.numdam.org/item/SB_1976-1977__19__19_0/

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