proposition: Lemma sumf_cancel3 T1 T2 (e1 n1 f1 : T1 -> T1) (e2 n2 f2 : T2 -> T2) : cancel3 e1 n1 f1 -> cancel3 e2 n2 f2 -> cancel3 (sumf e1 e2) (sumf n1 n2) (sumf f1 f2).
proof: Proof. by move => can1 can2 [x|x] /=; rewrite ?can1 ?can2. Qed.
imports: mathcomp(all_ssreflect) GraphTheory(edone preliminaries bij) fourcolor(hypermap geometry cfmap jordan color coloring combinatorial4ct) fourcolor(walkup)