@article{10_4153_CMB_1982_035_2,
     author = {Warren, Richard H.},
     title = {Discrete {Sets} and {Discrete} {Maps}},
     journal = {Canadian mathematical bulletin},
     pages = {242--244},
     year = {1982},
     volume = {25},
     number = {2},
     doi = {10.4153/CMB-1982-035-2},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1982-035-2/}
}