export declare type Defined<T> = T extends undefined ? never : T;
export declare type MinusKeys<T, U> = Pick<T, Exclude<keyof T, keyof U>>;
export declare type MergedProperties<T, U> = {
    [K in keyof T & keyof U]: undefined extends T[K] ? Defined<T[K] | U[K]> : T[K];
};
export declare function extend<A extends object, B extends object>(a: Readonly<A>, ...os: Array<Readonly<B>>): Readonly<Pick<A, Exclude<keyof A, keyof B>> & Pick<B, Exclude<keyof B, keyof A>> & MergedProperties<B, A>>;