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Recently I’m studying 3SAT problem, which is a NP-complete problem. I feel that it’s easy to find a boolean formula which is satisfiable,but how about boolean formulas which are unsatisfiable， namely 3-co-SAT problem. Can you help me provide some examples of 3-co-SAT?

The definition of 3SAT problem is supplemented here, which is quoted from the book Computational Theory.

3SAT = { is a satisfiable 3cnf-formula}

Then the definition of 3-co-SAT is

3-co-SAT = { is an unsatisfiable 3cnf-formula}

Is there any problem about the definition of the above sat, 3-co-sat problem?

Can you help me provide some examples of 3-co-SAT?