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Feb 19, 2019 at 8:28 vote accept DLIN
Jan 24, 2019 at 1:39 comment added Deane Yang @PiotrHajlasz, my guess is that the best constant corresponds to the constant curvature cases. The exponential factor seems to arise from the volume of a hyperbolic ball with radius $r$. But this is all speculation.
Jan 23, 2019 at 23:44 comment added Piotr Hajlasz @DeaneYang Relative isoperimetric inequality for Ricci bounded below was proved by Buser. Buser's inequality is equivalent to a Poincare inequality. Ricci implies that the measure is doubling (Bishop–Gromov comparison theorem) and doubling plus Poincare implies the right Sobolev inequality. However, I am not sure if this gives the best constant as in the theorem stated in my answer.
Jan 23, 2019 at 20:58 comment added Deane Yang Federer-Fleming proved that the best local Sobolev constant is equal to the best constant for the local isoperimetric inequality. A local isoperimetric inequality is known to hold in a neighborhood of a point, where the constant depends on a lower bound of Ricci and a lower bound, as a function of $r < 0$, on the volume of a geodesic ball of radius $r$ centered at that point. Alas, I don't remember the references for this.
Jan 23, 2019 at 1:56 history edited Piotr Hajlasz
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Jan 16, 2019 at 15:22 history edited Piotr Hajlasz CC BY-SA 4.0
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Jan 16, 2019 at 13:06 answer added Piotr Hajlasz timeline score: 3
Jan 16, 2019 at 12:08 history edited DLIN
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Jan 16, 2019 at 10:33 history asked DLIN CC BY-SA 4.0