... This is the polyhedral version of Withney's umbrella. We will say

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...This is the polyhedral version of Withney's umbrella. It looks like this surface was made from plywood, but that's because Fred (click and forget), who made all these images in three hours' time, hadn't yet found the routine in the documentation that created faces. So he used ultra-flat thingamajigs. - Tardy will do that better. Me, I don't have the time.... Smooth Version