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:
彼得森國際經濟研究所統計學家格雷格·奧克萊爾（Greg Auclair）告訴BBC 事實查核稱，過去一年美國的外國投資確實有所增加。但他警告，白宮追蹤器 （White House Tracker）「包含可能不會實現的承諾」，例如歐盟貿易協議因格陵蘭緊張局勢而凍結，並在今年2月因特朗普的關稅威脅再度中止。
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