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A fundamental tool in statistical mechanics and probabilistic combinatorics (especially random graphs and the probabilistic method), the Ahlswede–Daykin inequality , also known as the four functions theorem (or inequality), is a correlation-type inequality for four functions on a finite distributive lattice. It states that if are nonnegative functions on a finite distributive lattice such that : for all ''x'', ''y'' in the lattice, then : for all subsets ''X'', ''Y'' of the lattice, where : and : : The Ahlswede–Daykin inequality can be used to provide a short proof of both the Holley inequality and the FKG inequality. It also implies the Fishburn–Shepp inequality. For a proof, see the original article or . ==Generalizations== The "four functions theorem" was independently generalized to 2''k'' functions in and . 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Ahlswede–Daykin inequality」の詳細全文を読む スポンサード リンク
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