@article{10_4153_CMB_1990_080_1,
     author = {McCool, James},
     title = {The {Coherence} {Number} of {2-Groups}},
     journal = {Canadian mathematical bulletin},
     pages = {503--508},
     year = {1990},
     volume = {33},
     number = {4},
     doi = {10.4153/CMB-1990-080-1},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1990-080-1/}
}