import { type Observable } from 'rxjs';
export declare function reduceArray<T>(reduceFn: (acc: T, item: T, index: number) => T): (source: Observable<T[]>) => Observable<T>;
export declare function reduceArray<T, R = T>(reduceFn: (acc: R, item: T, index: number) => R, initialValue: R): (source: Observable<T[]>) => Observable<R>;