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In descriptive set theory, a tree over a product set is said to be homogeneous if there is a system of measures . * The measures are in some sense compatible under restriction of sequences: if , then . * If is in the projection of , the ultrapower by is wellfounded. An equivalent definition is produced when the final condition is replaced with the following: * There are such that . This condition can be thought of as a sort of countable completeness condition on the system of measures. is said to be -homogeneous if each is -complete. Homogeneous trees are involved in Martin and Steel's proof of projective determinacy. ==References== * 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「homogeneous tree」の詳細全文を読む スポンサード リンク
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