Homomorphisms of complete n-partite graphs. Girse, Robert D. — 1986 International Journal of Mathematics and Mathematical Sciences
A digraph equation for homomorphic images. Girse, Robert D.; Gillman, Richard A. — 1986 International Journal of Mathematics and Mathematical Sciences
Homomorphisms and related contractions of graphs. Girse, Robert D.; Gillman, Richard A. — 1988 International Journal of Mathematics and Mathematical Sciences