/**
 * Given a map of arrays, appends a value to the array at the given key.
 * If no array exists at that key, one is created and the value appended.
 * @param map Map of arrays
 * @param key Key to append the value at
 * @param value Value to append
 */
export declare function appendAtKey<K, V>(map: Map<K, V[]>, key: K, value: V): V[];