declare const isNumber: (value?: any) => value is number;
declare const isFunction: (value?: any) => value is (...args: any[]) => any;
declare const isPlainObject: (value: any) => boolean;
declare const isString: (value?: any) => value is string;
declare const isUndefined: (value?: any) => value is undefined;

export { isFunction, isNumber, isPlainObject, isString, isUndefined };