export declare class MultiMap<K, V> {
    private _map;
    add(key: K, value: V): void;
    add_all(key: K, values: Iterable<V>): void;
    delete(key: K, value: V): V | undefined;
    delete_all(key: K): Set<V> | undefined;
    clear(): void;
    group(key: K): Set<V>;
    has(key: K, value: V): boolean;
    hasKey(key: K): boolean;
    get keys(): IterableIterator<K>;
    get keyCount(): number;
    get size(): number;
    grouped(): IterableIterator<[K, Set<V>]>;
    items(): IterableIterator<[K, V]>;
}