fact: Definition sumA' {A B C} (x: (A + B) + C): A + (B + C) := match x with inr x => inr (inr x) | inl (inr x) => inr (inl x) | inl (inl x) => inl x end.
imports: Coq(Setoid CMorphisms) mathcomp(all_ssreflect) GraphTheory(edone preliminaries)