What does pi(c) stand for? It's not in your legend. Also, since you stay that only the bounding box with the highest IOU is backprogated, then why does the loss function sum over all bounding boxes. Thank you.
There are many interesting considerations to be made when choosing an appropriate loss/cost/energy function which I believe are easiest to understand when used with examples. Is there a way for you (the author) to consider previewing examples and, if you like them or not, add them to the book?