import { type Undefinable } from './undefinable.js';
/**
 *  Return one of this pattern:
 *
 *  1. a=others, b=undefined => _a_
 *  2. a=undefined, b=others => _b_
 *  3. Others => `undefined`
 */
export declare function xorForUndefinable<T>(a: Undefinable<T>, b: Undefinable<T>): Undefinable<T>;