@article{10_4153_CJM_1977_132_2,
     author = {Hartley, Richard and Murasugi, Kunio},
     title = {Covering {Linkage} {Invariants}},
     journal = {Canadian journal of mathematics},
     pages = {1312--1339},
     year = {1977},
     volume = {29},
     number = {6},
     doi = {10.4153/CJM-1977-132-2},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1977-132-2/}
}