@incollection{JEDP_1988____A6_0,
     author = {Dencker, Nils},
     title = {The propagation of polarization in double refraction},
     booktitle = {},
     series = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {6},
     pages = {1--9},
     publisher = {Ecole polytechnique},
     year = {1988},
     mrnumber = {90d:58150b},
     language = {en},
     url = {http://www.numdam.org/item/JEDP_1988____A6_0/}
}