fact: Definition avoid_one (G : hypermap) := forall z x y : G , ~~ cnode z x -> ~~ cnode z y -> connect (restrict [predC cnode z] clink) x y.
imports: mathcomp(all_ssreflect) GraphTheory(edone preliminaries digraph sgraph) fourcolor(hypermap geometry jordan color coloring combinatorial4ct) GraphTheory(hmap_ops)