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Exponents of Diophantine Approximation in Dimension Two

Published online by Cambridge University Press:  20 November 2018

Michel Laurent*
Affiliation:
Institut deMathématiques de Luminy, 13288 Marseille Cedex 9, FRANCE, [email protected]
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Abstract

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Let $\Theta \,=\,\left( \alpha ,\,\beta \right)$ be a point in ${{\text{R}}^{2}}$, with $1,\,\alpha ,\,\beta $ linearly independent over $\mathrm{Q}$. We attach to $\Theta $ a quadruple $\Omega \left( \Theta \right)$ of exponents that measure the quality of approximation to $\Theta $ both by rational points and by rational lines. The two “uniform” components of $\Omega \left( \Theta \right)$ are related by an equation due to Jarník, and the four exponents satisfy two inequalities that refine Khintchine's transference principle. Conversely, we show that for any quadruple $\Omega $ fulfilling these necessary conditions, there exists a point $\Theta \,\in \,{{\text{R}}^{2}}$ for which $\Omega \left( \Theta \right)\,=\,\Omega $.

Type
Research Article
Copyright
Copyright © Canadian Mathematical Society 2009

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