/**
 * ITEMS NESTED BY A PARENT ID, each drawn exactly once. A missing or self parent leaves an item at
 * the top; a parent loop promotes its first item and drops the closing link.
 */
export interface Forest<T> {
    /** In the caller's order. */
    roots: T[];
    /** In the caller's order. */
    children: (item: T) => T[];
}
export declare function forest<T>(items: readonly T[], idOf: (item: T) => string, parentOf: (item: T) => string | null | undefined): Forest<T>;