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Apr 19, 2010 at 14:47 comment added Keenan Kidwell @Pete Yeah, I thought about that as soon as I posted my response. I'm also not really sure what Jose has in mind, but it's good to point this out, that there is one obvious locally compact topology on $\overline{\mathbb{Q}}$.
Apr 19, 2010 at 14:32 comment added Pete L. Clark @KK: As with the integers, you could put the discrete norm on $\overline{\mathbb{Q}}$ and then it becomes locally compact and complete, with natural (Haar) measure being the counting measure. This feels like a rather trivial answer, but I can't tell from the question exactly what Jose has in mind.
Apr 19, 2010 at 11:59 comment added Keenan Kidwell The fact that the set of algebraic numbers is countable is not what precludes applying the usual integration machinery to it. The additive group of integers is a perfectly good (countable) locally compact group and people do Fourier analysis on it all the time. The problem with $\overline{\mathbb{Q}}$ is that it fails to be locally compact in any of its usual topologies.
Apr 19, 2010 at 11:57 history edited Gerald Edgar CC BY-SA 2.5
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Apr 19, 2010 at 11:52 history answered Gerald Edgar CC BY-SA 2.5