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In mathematics, the Tarski–Seidenberg theorem states that a set in (''n'' + 1)-dimensional space defined by polynomial equations and inequalities can be projected down onto ''n''-dimensional space, and the resulting set is still definable in terms of polynomial identities and inequalities. The theorem — also known as the Tarski–Seidenberg projection property — is named after Alfred Tarski and Abraham Seidenberg. It implies that quantifier elimination is possible over the reals, that is that every formula constructed from polynomial equations and inequalities by logical connectors ∨ (''or''), ∧ (''and''), ¬ (''not'') and quantifiers ∀ (''for all''), ∃ (''exists'') is equivalent with a similar formula without quantifiers. An important consequence is the decidability of the theory of real-closed fields. ==Statement== A semialgebraic set in R''n'' is a finite union of sets defined by a finite number of polynomial equations and inequalities, that is by a finite number of statements of the form : and : for polynomials ''p'' and ''q''. We define a projection map ''π'' : R''n''+1 → R''n'' by sending a point (''x''1,...,''x''''n'',''x''''n''+1) to (''x''1,...,''x''''n''). Then the Tarski–Seidenberg theorem states that if ''X'' is a semialgebraic set in R''n''+1 for some ''n'' > 1, then ''π''(''X'') is a semialgebraic set in R''n''. 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「Tarski–Seidenberg theorem」の詳細全文を読む スポンサード リンク
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