There are even worse mistakes in the pictures; I'll fix them pretty soon. There are certain arbitrary conventions in this game, but one should handle them consistently and I didn't. It's easy to get the conventions right when I'm writing things on paper and can look at all the diagrams at once, but it's harder when I'm drawing diagrams in LaTeX, using Irfanview to create png files from them, and writing a lecture in LaTeX on the forum, which I can only look at when it's done!

Now you folks are exploring the various subtleties of this subject and seeing how tricky it is. I'll let you know when I fix this lecture; then everything should make sense!