@article{SD_1967-1968__21_1_A7_0,
     author = {Lefebvre, Pierre},
     title = {Demi-groupes et anneaux de fractions},
     journal = {S\'eminaire Dubreil. Alg\`ebre et th\'eorie des nombres},
     note = {talk:7},
     pages = {1--9},
     publisher = {Secr\'etariat math\'ematique},
     volume = {21},
     number = {1},
     year = {1967-1968},
     zbl = {0184.06305},
     language = {fr},
     url = {http://www.numdam.org/item/SD_1967-1968__21_1_A7_0/}
}