interface EventEmitter<T extends Record<string, unknown[]>> {
  on<K extends string, L extends unknown[]>(ev: K, callback: (...args: L) => void): asserts this is EventEmitter<T & {[P in K]: L}>;
  off<K extends keyof T>(ev: K): asserts this is EventEmitter<Omit<T, K>>;
  emit<K extends keyof T>(ev: K, ...args: T[K]): void;
}