十年后，我们可能不止需要 iPhone 了。
How did Nasa's Suni and Butch fill nine months in space?
，更多细节参见搜狗输入法下载
This formula is satisfiable because if we set to b to true and a to false, then the whole formula is true. All other assignments make the formula false, but it doesn't change that the formula is satisfiable as long as there is at least one assignment makes the formula true.
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