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Published online by Cambridge University Press: 24 October 2008
Let
be a non-degenerate quadratic form with integral coefficients. Further, let Q(x) be a zero form, i.e. let there exist x ≠ 0 in ℤn such that Q(x) = 0. Then we know from Cassels[2], (Davenport[6] and ‘a slightly more general result’ from Birch and Davenport [1]) that there exists a ‘small’ solution x in ℤn of the equation Q(x) = 0; more precisely, if
then there exists x ≠ 0 in ℤn such that Q(x) = 0 and further
(Here, and throughout this section, k will denote a number, not necessarily the same at each occurrence, which depends only on n.) An analogue of this estimate for ‘integral’ quadratic forms over algebraic number fields was proved in [8], with the exponent (n − 1)/2 remaining intact.