Section Weight.
Variable A : Type.
Variable eqA_dec : forall a b : A, {a = b} + {a <> b}.

Theorem fold_plus_split :
forall (B : Type) (l : list B) (c : nat) (f : B -> nat),
c + fold_left (fun (a : nat) (b : B) => a + f b) l 0 =
fold_left (fun (a : nat) (b : B) => a + f b) l c.