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<p>Finally, this book is a living document. What that means is that on occasion we will make updates to the book such as fixing typos and including additional detail or activities. When substantial changes are made, we will create new support materials such as an accompanying video. However, it would be impossible to record a new video every time we make a minor change to an activity, therefore, sometimes there may be slight differences between the videos and the content of this book. Where there are dif