export declare function isString(o: any): o is string;
export declare function isBool(o: any): o is boolean;
export declare function isFunction(o: any): o is Function;
export declare function isNumber(o: any): o is number;
export declare function isHTMLElement(o: any): o is HTMLElement;
export declare function isEmptyArray<T>(array: T[]): boolean;
export declare function isLetterWithNum(str: string): boolean;