@article{GDZPPN002026236, title = {The Lattice of Natural Partial Orders.}, journal = {Aequationes mathematicae}, volume = {8}, year = {1972}, pages = {95-102}, zbl = {0251.06005}, url = {http://dml.mathdoc.fr/item/GDZPPN002026236} }
Avann, S.P. The Lattice of Natural Partial Orders.. Aequationes mathematicae, Tome 8 (1972) pp. 95-102. http://gdmltest.u-ga.fr/item/GDZPPN002026236/