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May 2, 2013 at 14:42 vote accept Peter Crooks
May 1, 2013 at 23:36 comment added Will Sawin What about disjoint union of infinitely many affines? I guess that's not really a variety.
May 1, 2013 at 23:17 history edited Steven Landsburg CC BY-SA 3.0
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May 1, 2013 at 23:03 history edited Steven Landsburg CC BY-SA 3.0
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May 1, 2013 at 20:36 comment added Sam Gunningham @Dan: Sorry, didn't see your comment in time.
May 1, 2013 at 20:35 comment added Sam Gunningham Can't you just take open affines in each irreducible component which do not intersect any other component? Then the union of such will be disjoint.
May 1, 2013 at 20:33 comment added Dan Petersen You can trivially reduce to the case when the connected components of $X$ are irreducible: just shrink $X$ to a smaller variety $X'$ by throwing out all points lying on more than one irreducible component. Then $X'$ is open and dense in $X$ and it suffices to find a dense affine in $X'$.
May 1, 2013 at 20:02 comment added Peter Crooks Good point! The irreducible case is straightforward, but the more general case is subtle. I suppose that if the irreducible components coincided with the connected components, then the above argument would work.
May 1, 2013 at 19:53 comment added Angelo This must be done a little more carefully: the union is not necessarily affine, or even a subvariety.
May 1, 2013 at 19:38 vote accept Peter Crooks
May 1, 2013 at 20:00
May 1, 2013 at 19:33 history answered Steven Landsburg CC BY-SA 3.0