Visit Pexel From Here
限制：数据范围不能太大，否则空间浪费
，更多细节参见im钱包官方下载
There is a special form for boolean formulas called "Conjunctive Normal Form" (CNF). A problem in this form consists of clauses connected with and operators, where each clause only contains variables connected with or operators. The variables can appear negated, but only variables can be directly negated, something like !(a && b) is not allowed. An example boolean formula in CNF form is:
FirstFT: the day's biggest stories