# What is the lesson here?
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:
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新中国成立后，葛洲坝、三峡大坝等大型工程逐步建设，几十万宜昌人民离开故土，搬出库区。他们舍小家、为大家，重新扎根开花，就像蜡梅一样昂扬生长。
其次，大厂们也在“推波助澜”。