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Mar 27, 2021 at 21:13 comment added Mateusz Kwaśnicki Sorry for the delay. I tried to understand what the double integral really means, and I failed. If we integrate it over $x$, this seems to give the quadratic form corresponding to $(-\Delta)^{2s}$ (with $2s$ rather than $s$ in the exponent), which seems slightly odd. I'm afraid I cannot help much here, but if I may ask, out of curiosity: how did you come up with this expression? And why do you expect the claim to be true? I think I must be missing something obvious here.
Mar 25, 2021 at 6:22 comment added Zac @MateuszKwaśnicki Ok, thanks! Please, let me know
Mar 24, 2021 at 13:03 comment added Mateusz Kwaśnicki Ah, I realise I did not read your question correctly. Let me think for a minute.
Mar 24, 2021 at 12:20 comment added Zac @MateuszKwaśnicki Thank you! What if I add another assumption, for example that $(-\Delta)^s u = 1$?
Mar 24, 2021 at 12:09 comment added Mateusz Kwaśnicki Of course not! Take any smooth $u_0$ with compact support. Then the integral is finite, and so $u = \lambda u_0$ for an appropriate $\lambda$ has the integral equal to $C$, but it is not of the desired form.
Mar 24, 2021 at 12:04 history asked Zac CC BY-SA 4.0