@article{10_4153_CJM_1972_042_0,
     author = {Sobczyk, Andrew and Jr., James O. Gettys},
     title = {Extended {Chromatic} {Polynomials}},
     journal = {Canadian journal of mathematics},
     pages = {492--501},
     year = {1972},
     volume = {24},
     number = {3},
     doi = {10.4153/CJM-1972-042-0},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1972-042-0/}
}