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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Better-quasi-ordering ： ウィキペディア英語版 Better-quasi-ordering In order theory a better-quasi-ordering or bqo is a quasi-ordering that does not admit a certain type of bad array. Every bqo is well-quasi-ordered. == Motivation == Though wqo is an appealing notion, many important infinitary operations do not preserve wqoness. An example due to Richard Rado illustrates this.〔 In a 1965 paper Crispin Nash-Williams formulated the stronger notion of bqo in order to prove that the class of trees of height ω is wqo under the topological minor relation.〔 Since then, many quasi-orders have been proven to be wqo by proving them to be bqo. For instance, Richard Laver established Fraïssé's conjecture by proving that the class of scattered linear order types is bqo.〔 More recently, Carlos Martinez-Ranero has proven that, under the Proper Forcing Axiom, the class of Aronszajn lines is bqo under the embeddability relation.〔 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「Better-quasi-ordering」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.