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For SAT problems with 10 variables and 200 clauses, it usually output SAT as expected, but the assignment was never valid (Examples: first, second). Once it claimed a SAT formula was UNSAT. For this reason I didn't bother testing with more variables for the SAT case.
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第三十七条 纳税人发生应税交易，应当向购买方开具发票。有下列情形之一的，不得开具增值税专用发票：。同城约会对此有专业解读
* 获取数字的第digit位（从右往左，0表示个位）