@article{NSJOM_1988_18_2a_0,
     author = {H\'ebert Michel},
     title = {Sur l' 

 existence des alg\`ebres libres pour les th\'eories n\'egatives},
     journal = {Novi Sad Journal of Mathematics},
     pages = {1-23},
     publisher = {mathdoc},
     volume = {18},
     number = {2},
     year = {1988},
     url = {http://geodesic.mathdoc.fr/item/NSJOM_1988_18_2a_0/}
}