@article{04170933, title = {Homomorphisms and related contractions of graphs.}, journal = {International Journal of Mathematics and Mathematical Sciences}, volume = {11}, year = {1988}, pages = {95-100}, doi = {10.1155/S0161171288000146}, zbl = {0712.05028}, language = {en}, url = {http://dml.mathdoc.fr/item/04170933} }
Girse, Robert D.; Gillman, Richard A. Homomorphisms and related contractions of graphs.. International Journal of Mathematics and Mathematical Sciences, Tome 11 (1988) pp. 95-100. doi : 10.1155/S0161171288000146. http://gdmltest.u-ga.fr/item/04170933/