/**
 * Crossref: the DOI registry's bibliographic metadata. get_paper uses it only
 * when OpenAlex has no record for a DOI. Crossref asks clients to name
 * themselves in the User-Agent, which core.ts does.
 */
import { type PaperContext } from "./core.js";
import type { PaperRecord } from "./records.js";
export declare function getCrossrefWork(ctx: PaperContext, doi: string): Promise<PaperRecord | null>;