For your any problem regarding book you can inform us. you will try to response of your email withing short time. One thing keep in mind we write book even for very novice people if you have primary knowledge than you have to collect our advance book. Even if you have advance knowledge you should not buy advance level book . you can collect professional level book. we always encourage your feedback. please send any suggestion for book . we always try to write best one but unfortunately for many reason few mistake occurs so we are very sorry for that.