import Sequence from "./Sequence";
export declare class Single {
    /**
     * Returns the single element of the sequence or throws error if the sequence has more than
     * one element or none at all. If a `predicate` is passed returns the single element matching
     * the predicate or throws an error if more or less than one element match the predicate.
     *
     * @param {(value: T) => boolean} predicate
     * @returns {T}
     */
    single<T>(this: Sequence<T>, predicate?: (value: T) => boolean): T;
}