fact: Fixpoint Sum_upto (f : nat -> R) (n : nat) {struct n} : R := match n with | O => [0] | S x => f x[+]Sum_upto f x end.
imports: CoRN.tactics.CornTac CoRN.algebra.CSums CoRN.algebra.CAbMonoids Coq.Sorting.Permutation CoRN.util.SetoidPermutation Coq.Setoids.Setoid Coq.Classes.Morphisms Coq(Lia)