@article{ASENS_1920_3_37__107_0,
     author = {Clairin, Jean},
     title = {Sur les invariants des caract\'eristiques des \'equations aux d\'eriv\'ees partielles \`a deux variables ind\'ependantes},
     journal = {Annales scientifiques de l'\'Ecole Normale Sup\'erieure},
     pages = {107--116},
     year = {1920},
     publisher = {Elsevier},
     volume = {3e s{\'e}rie, 37},
     doi = {10.24033/asens.721},
     language = {fr},
     url = {https://www.numdam.org/articles/10.24033/asens.721/}
}