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Projective degenerations of K3 surfaces, Gaussian maps, and Fano threefolds

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In this article we exhibit certain projective degenerations of smoothK3 surfaces of degree 2g−2 in ℙg (whose Picard group is generated by the hyperplane class), to a union of two rational normal scrolls, and also to a union of planes. As a consequence we prove that the general hyperplane section of suchK3 surfaces has a corank one Gaussian map, ifg=11 org≥13. We also prove that the general such hyperplane section lies on a uniqueK3 surface, up to projectivities. Finally we present a new approach to the classification of prime Fano threefolds of index one, which does not rely on the existence of a line.

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Oblatum 1-II-1993 & 24-V-1993

Research supported in part by NSF grant DMS-9104058

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Ciliberto, C., Lopez, A. & Miranda, R. Projective degenerations of K3 surfaces, Gaussian maps, and Fano threefolds. Invent Math 114, 641–667 (1993). https://doi.org/10.1007/BF01232682

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