fact: Definition to_associational (n:nat) (xs:list Z) : list (Z*Z) := combine (map weight (List.seq 0 n)) xs.
imports: Coq.ZArith.ZArith Coq.Lists.List Coq.Setoids.Setoid Coq.Classes.Morphisms Coq.QArith.QArith_base Coq.QArith.Qreduction Coq.QArith.Qround