export declare const isString: (value: unknown) => value is string;
export declare const isPlainObject: (value: unknown) => value is object;
export declare function flattenTree<T>(root: T, children: (node: T) => Iterable<T>, predicate?: (node: T) => boolean): Set<T>;
export declare function concatIterables<T>(...iterables: Iterable<T>[]): Iterable<T>;
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