@article{10_4064_ap_49_1_81_92,
     author = {Piotr Rybka},
     title = {Propagation of weak singularities on characteristic surfaces of non-constant multiplicity},
     journal = {Annales Polonici Mathematici},
     pages = {81--92},
     publisher = {mathdoc},
     volume = {49},
     number = {1},
     year = {1988},
     doi = {10.4064/ap-49-1-81-92},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-49-1-81-92/}
}