@article{TAC_2008_20_a8,
     author = {Marta Bunge},
     title = {Fundamental pushout toposes},
     journal = {Theory and applications of categories},
     pages = {186--214},
     publisher = {mathdoc},
     volume = {20},
     year = {2008},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/TAC_2008_20_a8/}
}