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Sep 11, 2018 at 17:35 vote accept Chuck Newton
Sep 10, 2018 at 23:22 answer added Anthony Quas timeline score: 2
Sep 10, 2018 at 22:21 comment added Anthony Quas I'm not aware of any prior work on this, but as I mentioned, I believe Strassen's theorem, giving conditions for the existence of monotonic couplings is likely to be useful.
Sep 10, 2018 at 22:19 comment added Chuck Newton Yes, that sounds perfect. Is there any prior work on this kind of thing? (I'd never heard of Strassen's theorem, will give it a look)
Sep 10, 2018 at 22:19 comment added Anthony Quas I believe the answer to my attempted reformulation of your question is that the possible pdf's of $h(X,X')$ are precisely those pdf's $g$ satisfying your conditions: $(\int_I f(x)\,dx)^2\le \int_I g(x)\,dx\le 1-(1-\int_I f(x)\,dx)^2$ for all events $I$. If this is right, the proof should probably go by Strassen's theorem.
Sep 10, 2018 at 22:16 comment added Anthony Quas I suspect the question you really want to ask is the following: consider possible rules $h\colon\mathbb R^2\to\mathbb R$ where $h(x,x')\in\{x,x'\}$ (or maybe a random generalization I'll mention below). Then what are the possible pdf's of $h(X,X')$, where $X$ and $X'$ are independent samples from the pdf $f$. Here $h$ is "picking" between $x$ and $x'$. The random generalization is $h(x,x',z)\in\{x,x'\}$ where $z\in[0,1]$ is an independent Unif[0,1] random variable.
Sep 10, 2018 at 21:24 history edited Chuck Newton CC BY-SA 4.0
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Sep 10, 2018 at 20:23 history asked Chuck Newton CC BY-SA 4.0