@article{10_4153_CMB_1982_065_1,
     author = {Karnik, S. M. and Willard, S.},
     title = {Natural {Covers} and {R-Quotient} {Maps}},
     journal = {Canadian mathematical bulletin},
     pages = {456--461},
     year = {1982},
     volume = {25},
     number = {4},
     doi = {10.4153/CMB-1982-065-1},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1982-065-1/}
}