/**
 * Returns a new set representing the union of a and b.
 */
export declare function union<T>(a: Set<T>, b: Iterable<T>): Set<T>;
/**
 * Adds all items from the set b to a.
 */
export declare function addAll<T>(target: Set<T>, source: Iterable<T>): void;
/**
 * Returns whether two sets are equal
 */
export declare function equal<T>(a: Set<T>, b: Set<T>): boolean;