Put
Where e(x) = e2πi∕p and xx′≡ yy′≡ 1 (mod p), Mordell has conjectured
that S(c) = O(p). The writer shows first, by an elementary argument that
S(c) = O(p3∕2). Next he proves, using a theorem of Lang and Weil that
S(c) = O(p11∕8). Finally he proves that S(c) = O(p5∕4); the proof makes use of the
estimate
where ψ(a) is the Legendre symbol and f(x) is a polynomial of the fourth
degree.
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