A little bit of a note about programming, you can understand recommender systems and the math and algorithms behind them without ever getting into code. And, we found from experience that lots of people want exactly this background, some of them may be very comfortable with coding and not want to take the time, others may be coming from a different perspective, whether you're coming from more of a mathematical perspective, from a business and marketing perspective, and this course, as it's designed today, is designed to help all of you who don't want to code, get through a deep understanding of recommender systems. At the same time, we recognize that for many people, actually building them, is a wonderful way to aid in understanding, and frankly is a separately useful skill. Originally, when we did this course the first time, we set it out with two tracks, a concepts track and a programming track, and the programming track was a set of extra work for people who wanted to learn the programming.