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== The Problem == | |||
<math> | Let <math>[3]^n</math> be the set of all length <math>n</math> strings over the alphabet <math>1, 2, 3</math>. A ''combinatorial line'' is a set of three points in <math>[3]^n</math>, formed by taking a string with one or more wildcards in it, e.g., <math>112*1**3\ldots</math>, and replacing those wildcards by <math>1, 2</math> and <math>3</math>, respectively. In the example given, the resulting combinatorial line is: | ||
$$ | |||
\{ 11211113\ldots, 11221223\ldots, 11231333\ldots \} | |||
$$ | |||
The Density Hales-Jewett theorem asserts that for any $\delta > 0$, | |||
for sufficiently large $n = n(\delta)$, all subsets of $[3]^n$ of size | |||
at least $\delta 3^n$ contain a combinatorial line, | |||
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* [http://meta.wikimedia.org/wiki/Help:Contents Wiki user's guide] | |||
Revision as of 16:40, 8 February 2009
The Problem
Let [math]\displaystyle{ [3]^n }[/math] be the set of all length [math]\displaystyle{ n }[/math] strings over the alphabet [math]\displaystyle{ 1, 2, 3 }[/math]. A combinatorial line is a set of three points in [math]\displaystyle{ [3]^n }[/math], formed by taking a string with one or more wildcards in it, e.g., [math]\displaystyle{ 112*1**3\ldots }[/math], and replacing those wildcards by [math]\displaystyle{ 1, 2 }[/math] and [math]\displaystyle{ 3 }[/math], respectively. In the example given, the resulting combinatorial line is: $$ \{ 11211113\ldots, 11221223\ldots, 11231333\ldots \} $$ The Density Hales-Jewett theorem asserts that for any $\delta > 0$, for sufficiently large $n = n(\delta)$, all subsets of $[3]^n$ of size at least $\delta 3^n$ contain a combinatorial line,
