@article{AFST_2013_6_22_5_1045_0,
     author = {Porter, Timothy},
     title = {Variations on a theme of homotopy},
     journal = {Annales de la Facult\'e des sciences de Toulouse : Math\'ematiques},
     pages = {1045--1089},
     publisher = {Universit\'e Paul Sabatier, Institut de math\'ematiques},
     address = {Toulouse},
     volume = {Ser. 6, 22},
     number = {5},
     year = {2013},
     doi = {10.5802/afst.1395},
     zbl = {1295.55001},
     mrnumber = {3154586},
     language = {en},
     url = {http://archive.numdam.org/articles/10.5802/afst.1395/}
}