@article{10_4153_CJM_1974_016_1,
     author = {Wells, Robert},
     title = {Double {Covers} and {Metastable} {Immersions} of {Spheres}},
     journal = {Canadian journal of mathematics},
     pages = {145--176},
     year = {1974},
     volume = {26},
     number = {1},
     doi = {10.4153/CJM-1974-016-1},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1974-016-1/}
}