III. a further result
Published online by Cambridge University Press: 24 October 2008
1. Let
where a > 0, be an indefinite quadratic form, so that d = b2 − 4ac > 0. A classical theorem of Minkowski states that, if (x0, y0) is any pair of real numbers, there are numbers (x, y) congruent (mod 1) to (x0, y0), such that
and, more recently, Davenport has shown that this theorem can be sharpened for certain special f, for instance that it is always possible to satisfy
† Davenport, , Proc. K. Ned. Akad. Wet. Amsterdam, 44 (1946), 815–21.Google Scholar
‡ Remak, , Jber. dtsch. MatVer. 44 (1934), 238–49.Google Scholar
§ This f(x, y) plays a special part in another lattice problem. See Segre, , Duke Math. J. (1945), 337–65.CrossRefGoogle Scholar
† See Fig. 1.
† To justify (3) a postiori we note the identity, which can be proved directly,
where ξ = 2as 1x + b(x + s 1y) + 2cy − f (s 11) and η = y − ½. The origin and (s 1, 1) correspond to ±(f(s 1, 1), ½) in (ξ, η) coordinates so that at the intersections ξ = 0, and f(x, y) = f(x − s 1,y − 1) = ¼e.
‡ See Fig. 2. The region ℒ is enclosed by the dense line.