@article{10_4153_CJM_1976_126_2,
     author = {Button, Robert Warren},
     title = {A {Non-Standard} {Characterization} of {Perfect} {Mappings}},
     journal = {Canadian journal of mathematics},
     pages = {1277--1279},
     year = {1976},
     volume = {28},
     number = {6},
     doi = {10.4153/CJM-1976-126-2},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1976-126-2/}
}