(** Adding a valuation function on all elements of a set. *)

Definition sum (f:elt -> nat)(s:t) := fold (fun x => plus (f x)) s 0.Notation compat_opL := (Proper (E.eq==>Logic.eq==>Logic.eq)).Notation transposeL := (transpose Logic.eq).

(* Specifications: *)
Lemma sum_plus : forall f g, Proper (E.eq==>Logic.eq) f -> Proper (E.eq==>Logic.eq) g -> forall s, sum (fun x =>f x+g x) s = sum f s + sum g s.
Lemma sum_filter : forall f : elt -> bool, Proper (E.eq==>Logic.eq) f -> forall s, (sum (fun x => if f x then 1 else 0) s) = (cardinal (filter f s)).
Lemma fold_compat : forall (A:Type)(eqA:A->A->Prop)(st:Equivalence eqA) (f g:elt->A->A), Proper (E.eq==>eqA==>eqA) f -> transpose eqA f -> Proper (E.eq==>eqA==>eqA) g -> transpose eqA g -> forall (i:A)(s:t),(forall x:elt, (In x s) -> forall y, (eqA (f x y) (g x y))) -> (eqA (fold f s i) (fold g s i)).
Lemma sum_compat : forall f g, Proper (E.eq==>Logic.eq) f -> Proper (E.eq==>Logic.eq) g -> forall s, (forall x, In x s -> f x=g x) -> sum f s=sum g s.