import type { AsyncOrSync } from "ts-essentials";
export declare function bys<T>(stream?: TransformStream<T, T>): TransformStream<T, T>;
export declare function bys<T, R>(stream: TransformStream<T, R>): TransformStream<T, R>;
export declare function bys<T, R>(fn: (s: ReadableStream<T>) => AsyncOrSync<ReadableStream<R>>): TransformStream<T, R>;