※ 引述《Jer1983 (stanley)》之銘言：
: Let A=[0,1]∩Q , Q: rational numbers
: If A is contained in (I_1) ∪ (I_2) ∪...∪ (I_n) , I_n are open intervals
: Show that m(I_1) + m(I_2) + ... + m(I_n) >= 1
: , where m is the length of interval.
寫 S = (I_1) ∪ (I_2) ∪...∪ (I_n), 則 A 為 S 之子集.
於是 cl(A) ＝ [0,1] 為 cl(S) 之子集, 接下來就..QED 了
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