import { IterableX } from '../../iterable/iterablex';
export declare function sumProto(this: IterableX<number>, fn?: (x: number) => number): number;
export declare function sumProto<T>(this: IterableX<T>, fn: (x: T) => number): number;
declare module '../../iterable/iterablex' {
    interface IterableX<T> {
        sum: typeof sumProto;
    }
}