Bemerkungen über den Zusammenhang der Flächen
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Klein (1874)
Mathematische Annalen
Burt Totaro (2009)
Bulletin de la Société Mathématique de France
We construct new birational maps between quadrics over a field. The maps apply to several types of quadratic forms, including Pfister neighbors, neighbors of multiples of a Pfister form, and half-neighbors. One application is to determine which quadrics over a field are ruled (that is, birational to the projective line times some variety) in a larger range of dimensions. We describe ruledness completely for quadratic forms of odd dimension at most 17, even dimension at most 10, or dimension 14....
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