@article{SJL_1964___1_72_0,
     author = {Leray, Jean and Waelbroeck, Lucien},
     title = {Norme formelle d'une fonction compos\'ee (pr\'eliminaire \`a l'\'etude des syst\`emes non lin\'eaires, hyperboliques non stricts)},
     journal = {S\'eminaire sur les \'equations aux d\'eriv\'ees partielles},
     pages = {72--82},
     year = {1964},
     publisher = {Coll\`ege de France},
     number = {1},
     language = {fr},
     url = {https://www.numdam.org/item/SJL_1964___1_72_0/}
}