@article{TAC_2013_28_a31,
     author = {Peter Johnstone},
     title = {The {Gleason} cover of a realizability topos},
     journal = {Theory and applications of categories},
     pages = {1139--1152},
     publisher = {mathdoc},
     volume = {28},
     year = {2013},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/TAC_2013_28_a31/}
}