@article{CMH_1955__29_139095,
     author = {P.J. Hilton},
     title = {On the homotopy groups of unions of spaces.},
     journal = {Commentarii mathematici Helvetici},
     pages = {59--92},
     publisher = {mathdoc},
     volume = {29},
     year = {1955},
     zbl = {0064.17203},
     url = {http://geodesic.mathdoc.fr/item/CMH_1955__29_139095/}
}