@article{AM2_1972__8_136273,
     author = {S.P. Avann},
     title = {The {Lattice} of {Natural} {Partial} {Orders.}},
     journal = {Aequationes mathematicae},
     pages = {95--102},
     publisher = {mathdoc},
     volume = {8},
     year = {1972},
     zbl = {0251.06005},
     url = {http://geodesic.mathdoc.fr/item/AM2_1972__8_136273/}
}