@article{PIM_1977_N_S_22_36_a18,
     author = {Peter Krenger and J\"urg R\"atz},
     title = {On {The} {Sup} {And} {Inf} {Invariance} {Of} {Some} {Separation} {Axioms}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {145 },
     publisher = {mathdoc},
     volume = {_N_S_22},
     number = {36},
     year = {1977},
     url = {http://geodesic.mathdoc.fr/item/PIM_1977_N_S_22_36_a18/}
}