Hi, I was wondering if you can explain exactly how the `add_face` function in the poly connectivity class works. I've been trying to understand how it works by reading the code, but I can't figure all the corner cases. I've also posted a question here ( https://computergraphics.stackexchange.com/questions/8771/halfedge-data-stru...) which also points the specific bit I don't understand. Can you help? Thank you so much.