若且唯若

Max 上課提到「若且唯若」在英文有縮寫 iff，然後說在中文他其實也想造一個字：

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重點是要對稱！所以英文版其實該用 fif 才對 XD。

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David Gries: "The notation iff is used for 'if and only if'. A few years ago, while lecturing in Denmark, I used fif instead, reasoning that since 'if and only if' was a symmetric concept its notation should be symmetric also. Without knowing it, I had punned in Danish and the audience laughed, for fif in Danish means 'a little trick.' I resolved thereafter to use fif so I could tell my little joke, but my colleagues talked me out of it."

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Quoted from The Computer Contradictionary by Stan Kelly-Bootle.