/**
 * Returns `arr` as is if none of the elements are `undefined`.
 * Otherwise returns a new array with only defined elements in `arr`.
 */
export declare function defined<T>(arr: (T | undefined)[]): T[];
export declare function areEqual<T>(arr1: readonly T[], arr2: readonly T[]): boolean;
export declare function zip<T1, T2>(a1: readonly T1[], a2: readonly T2[]): [T1, T2][];
export declare function last<T>(arr: T[]): T | undefined;
export declare function groupBy<T, K>(arr: readonly T[], keyFn: (el: T) => K): Map<K, T[]>;
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