/**
 * https://www.typescriptlang.org/docs/handbook/advanced-types.html#user-defined-type-guards
 */
export declare function isDefined<T>(value: T | undefined | null): value is T;
export declare function isNotDefined<T>(value: T | undefined | null): value is null | undefined;
export declare type Pair<A, B> = [A, B];
export declare type Optional<T> = T | undefined | null;