re in "figure D", including the concave ones http://img.tfd.com/ggse/a5/gsed_0001_0014_0_img3314.png
maybe to do this it would have to interpolate the curves in way that the second point subtracts form the first rather than add to become an oval?
this example also has 3 foci: F1 F2 F3
thanks for any help u can give
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