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--- Prefix 不 FU = "un-|not"
不 fu = "un-" prefix   Ref. 不 [un-]
不信 fushin distrust 信 [believe]  Ref. 不 [un-]
不眠 fumin insomnia 眠 [sleep]  Ref. 不 [un-]
不安 fuan uneasyness | unsecurity 安 [tranquil]  Ref. 不 [un-]