|
In set theory, a branch of mathematics, the Milner – Rado paradox, found by , states that every ordinal number α less than the successor ''κ''+ of some cardinal number κ can be written as the union of sets ''X''1,''X''2,... where ''X''''n'' is of order type at most ''κ''''n'' for ''n'' a positive integer. ==Proof== The proof is by transfinite induction. Let '''' be a limit ordinal (the induction is trivial for successor ordinals), and for each '''', let '''' be a partition of '''' satisfying the requirements of the theorem. Fix an increasing sequence cofinal in with . Note . Define: : and so ''''. Let be the order type of ''''. As for the order types, clearly . Noting that the sets form a consecutive sequence of ordinal intervals, and that each we get that: : 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「Milner–Rado paradox」の詳細全文を読む スポンサード リンク
|