You need to know: Notations: for the set of positive integers,
for the distance from real number x to the nearest integer. In addition, you need to know the concept of Hausdorff dimension of set
to understand the context.
Background: Let S be the set of pairs of real numbers such that
and
. For
, let
denote the set of points
for which there exists a positive constant
such that
for all
.
The Theorem: On 15th January 2010, Dzmitry Badziahin, Andrew Pollington, and Sanju Velani submitted to arxiv and the Annals of Mathematics a paper in which they proved that for any finite number of pairs from S, the set
is non-empty.
Short context: A real number x is said to be badly approximable if there exists a constant such that
for all
. Sets
are natural generalisations containing pairs
of simultaneously badly approximable numbers. The Theorem confirms a 1983 conjecture of Schmidt. In fact, Schmidt conjectured it for specific values
,
, and
, and even this remained open. Any counterexample to this conjecture would imply the famous Littlewood conjecture (see here), but the Theorem states that there is no counterexample. In fact, Badziahin, Pollington, and Velani proved a much stronger result that the set
is not only non-empty, but has Hausdorff dimension 2 – the same as the whole plane. In a later work, this result has been extended to higher dimensions.
Links: Free arxiv version of the original paper is here, journal version is here.
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