@article{10_4153_CJM_1981_009_7,
     author = {Hartley, Richard},
     title = {Knots with {Free} {Period}},
     journal = {Canadian journal of mathematics},
     pages = {91--102},
     year = {1981},
     volume = {33},
     number = {1},
     doi = {10.4153/CJM-1981-009-7},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1981-009-7/}
}