import type { Reducer } from "@thi.ng/transducers";
/**
 * Computes union of sets `a` and `b` and writes results to new set or
 * optionally given set `out` (assumed to be empty for correct results).
 *
 * @param a - first set
 * @param b - other set
 * @param out - result set
 */
export declare const union: <T>(a: Set<T>, b: Set<T>, out?: Set<T>) => Set<T>;
/**
 * Reducer version of {@link union}. If `src` is given returns the reduced union
 * of given inputs, else merely returns a reducer to be used with
 * [`reduce`](https://docs.thi.ng/umbrella/transducers/functions/reduce.html)
 * /
 * [`transduce`](https://docs.thi.ng/umbrella/transducers/functions/transduce.html)
 * functions.
 *
 * @param src - input collections
 */
export declare function unionR<T>(): Reducer<Iterable<T>, Set<T>>;
export declare function unionR<T>(src: Iterable<Iterable<T>>): Set<T>;
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