So a knife edge termination to a concave cavity is key in setiing up the swirl of a fluid tail.
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we are already starting to see this concave treatment of the truncation on hatch backs with their "visor" following the roof line to hang over the rear glass. And the sharp termination of the side lines at the rear bumper falling away at a sharp right angle to the "step" lift over area at the rear access.
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http://www.mooncraft.jp/yuratakuya/garage/prius/01.html
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