@article{TAC_2010_24_a0,
     author = {Stephen Lack and R.F.C. Walters and R.J. Wood},
     title = {Bicategories of spans as cartesian bicategories},
     journal = {Theory and applications of categories},
     pages = {1--24},
     publisher = {mathdoc},
     volume = {24},
     year = {2010},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/TAC_2010_24_a0/}
}