@article{10_4153_CJM_1977_004_3,
     author = {Walker, Marshall},
     title = {Homotopy {Pull-Backs} and {Applications} to {Duality}},
     journal = {Canadian journal of mathematics},
     pages = {45--64},
     year = {1977},
     volume = {29},
     number = {1},
     doi = {10.4153/CJM-1977-004-3},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1977-004-3/}
}