export declare function mergeDeep<T, S>(target: T, source: S): T & S;
export declare function mergeDeep<T, S1>(target: T, source1: S1): T & S1;
export declare function mergeDeep<T, S1, S2>(target: T, source1: S1, source2: S2): T & S1 & S2;
export declare function mergeDeep<T, S1, S2, S3>(target: T, source1: S1, source2: S2, source3: S3): T & S1 & S2 & S3;