@article{PORMA_1967__26_2_115018,
     author = {Hill, Paul},
     title = {Concerning anti-closed subsets in semigroups},
     journal = {Portugaliae mathematica},
     pages = {193--200},
     publisher = {mathdoc},
     volume = {26},
     number = {2},
     year = {1967},
     mrnumber = {0248264},
     zbl = {0183.02203},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1967__26_2_115018/}
}