"That was one about my idol," he told the Birmingham crowd. "And this is one he wrote," he said, launching into a cover of The Beatles' 1968 classic Revolution.
SAT (short for "satisfiability") is a logic problem that given a boolean formula, it asks whether the boolean formula has an assignment that makes the problem true. An example boolean formula is:
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一个秘鲁贫民窟的居民，在自己的房子里住了几十年，但当他拿着一张手写“地契”去银行贷款时，那张纸在银行眼里毫无价值。没有正式产权，就无法抵押贷款；没有贷款，就没有创业资本；没有资本，就只能在非正规经济中挣扎。这套住房对他来说只是资产，而不是资本，因为它无法进入市场体系，无法产生流动性，也无法参与资本计算。
int exchanged = 1; // 标记本轮是否发生交换