Sorry for having referred to the article for details towards the end. I now went and added a little more text to go with that last diagram. Because the reason for its hour glass look is not that there is a bottleneck in the extension process here, but because towards the right the diagram shows cocycles, and to the left it shows the homotopy fibers of these cocycles.I like the bottleneck in D=9 in the last diagram.
Thanks for the feedback.Man that's beautiful stuff.
Wish my math was up to the full details these days.
It taps out at RHS's - that's about my limit.