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Mar 20 at 12:50 answer added an_ordinary_mathematician timeline score: 2
Mar 14 at 21:41 comment added Gabriel Palau @ChristianRemling the no is for the first question I underestand. Any idea for the rest?
Mar 14 at 21:40 history edited Gabriel Palau CC BY-SA 4.0
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Mar 14 at 21:35 history edited YCor CC BY-SA 4.0
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Mar 14 at 21:25 comment added Gabriel Palau thanks to both for the comments
Mar 14 at 21:21 comment added Christian Remling No. $\{ f: \textrm{supp }f\subseteq [0,\infty) \}$ is a proper closed subspace of $L^2$ and $H$ is unitary.
Mar 14 at 21:21 comment added Aleksei Kulikov For the first question of course not. If $Hf$ is close to $g$, then (since $H$ is continuous) $f = (-H)Hf$ is close to $-Hg$, so we can approximate $g$ (and indeed be equal to it) if and only if $-Hg$ is $0$ on $\mathbb{R}_{-}$.
Mar 14 at 21:09 history edited Gabriel Palau CC BY-SA 4.0
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Mar 14 at 20:59 history asked Gabriel Palau CC BY-SA 4.0