Birational automorphisms of a double space and double quadric

It is proved that the groups of birational automorphisms are the same as the groups of biregular automorphisms for two series of Fano varieties of dimension 4 and higher: double spaces of index 1 and double quadrics of index 1. From this it follows that the varieties are not rational. The proof that the respective automorphism groups are the same extends the method of V.  A. Iskovskikh and Yu. I. Manin (the method of isolating and excluding maximal singularities) to arbitrary dimension.
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