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Jul 15, 2010 at 21:13 vote accept Izhar Oppenheim
Jul 15, 2010 at 14:09 comment added Charles Matthews (Continuation) Well, if the image contains the line as a matter of geometry, it looks like the pre-image of the line will be a curve on the quadric. Typically then there will not be a $K$-point mapping to a given $K$-point, unless we're in a trivial kind of situation. Izhar, where does this come from?
Jul 15, 2010 at 14:08 comment added Charles Matthews There is some geometry here. I don't see the initial motivation for the question, but here is the issue (and why I intuited the answer would be no in general). Using homogeneity, I thought the question came down to two things: does the image of a certain quadric surface in projective 4-space under a certain linear mapping contain a certain line? And given that it does, there is the rationality issue of whether there is a $K$-point mapping to a given $K$-point. (Continued)
Jul 15, 2010 at 13:53 history edited Pete L. Clark
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Jul 15, 2010 at 13:51 answer added Tom Goodwillie timeline score: 7
Jul 15, 2010 at 7:23 history asked Izhar Oppenheim CC BY-SA 2.5