@article{TAC_1999_5_a6,
     author = {Ronald Brown and Ghafar H. Mosa},
     title = {Double categories, 2-categories, thin structures and connections},
     journal = {Theory and applications of categories},
     pages = {163--175},
     publisher = {mathdoc},
     volume = {5},
     year = {1999},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/TAC_1999_5_a6/}
}