@article{JRAM_1979__310_152151,
     author = {Rudolf Wille and Ivan Rival},
     title = {Lattices freely generated by partially ordered sets: which can be },
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {56--80},
     year = {1979},
     volume = {310},
     zbl = {0416.06011},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1979__310_152151/}
}