（一）未经批准，安装、使用电网的，或者安装、使用电网不符合安全规定的；
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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"The scale is what makes it so extraordinary," Neil Redfern from the Council for British Archaeology says comparing HS2 to other big development projects.
A so-called "planetary nebula" is a confusing misnomer because these clouds have nothing to do with planets. As a medium-size star nears the end, it puffs out into a red giant — about 100 to 1,000 times its original size — eventually engulfing the space around it, including any nearby worlds.