While pleonastic negations are fairly common in French and somewhat so in several other languages, they are extremely infrequent in English. wonder and [wouldn't / shouldn't] be surprised are probably the only two expressions commonly followed by pleonastic not . These expressions work somewhat like the modal may in that may and may not have about the same meaning, the essential meaning of may encapsulating a sort of balancing act between the affirmative and the negative.
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