@article{PDML_1968__5_1_73_0,
     author = {Ravel, J.},
     title = {Th\'eorie axiomatique de l'essentialit\'e},
     journal = {Publications du D\'epartement de math\'ematiques (Lyon)},
     pages = {73--82},
     publisher = {Universit\'e Claude Bernard - Lyon 1},
     volume = {5},
     number = {1},
     year = {1968},
     mrnumber = {236074},
     zbl = {0169.02202},
     language = {fr},
     url = {http://www.numdam.org/item/PDML_1968__5_1_73_0/}
}