@article{SEDP_1975-1976____A1_0,
     author = {Nirenberg, L.},
     title = {Propagation of singularities for linear partial differential equations and reflections at a boundary},
     journal = {S\'eminaire \'Equations aux d\'eriv\'ees partielles (Polytechnique) dit aussi "S\'eminaire Goulaouic-Schwartz"},
     note = {talk:26},
     pages = {1--18},
     publisher = {Ecole Polytechnique, Centre de Math\'ematiques},
     year = {1975-1976},
     mrnumber = {611021},
     zbl = {0335.35081},
     language = {en},
     url = {http://archive.numdam.org/item/SEDP_1975-1976____A1_0/}
}