Published online by Cambridge University Press: 24 October 2008
The surfaces whose prime-sections are hyperelliptic curves of genus p have been classified by G. Castelnuovo. If p > 1, they are the surfaces which contain a (rational) pencil of conics, which traces the on the prime-sections. Thus, if we exclude ruled surfaces, they are rational surfaces. The supernormal surfaces are of order 4p + 4 and lie in space [3p + 5]. The minimum directrix curve to the pencil of conics—that is, the curve of minimum order which meets each conic in one point—may be of any order k, where 0 ≤ k ≤ p + 1. The prime-sections of these surfaces are conveniently represented on the normal rational ruled surfaces, either by quadric sections, or by quadric sections residual to a generator, according as k is even or odd.
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* If υ is a prime number, then a pencil of elliptic curves of order υ on a rational surface is represented in the plane, either by a pencil R of cubics, or by a Halphen pencil of curves of order 3υ with nine υ-ple base-points (not in general position). In the present case, however, υ = 3, it is easily shown that the Halphen pencil gives rise to surfaces having a unode: they are in fact surfaces discussed by P. Du Val, Proc. London Math. Soc. (2), 35 (1933), 1. Hence the only non-singular surfaces F′ arise from the pencil R of cubics given in the text.
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