@article{JRAM_1972__253_151198,
     author = {J\"urgen Schmidt},
     title = {Universal and internal properties of some extensions of partially orderd sets.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {28--42},
     publisher = {mathdoc},
     volume = {253},
     year = {1972},
     zbl = {0237.06001},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1972__253_151198/}
}