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am having problems understanding the difference between validity and satisfiability. Given the following:
(i) For all F, F is satisfiable or ~F is satisfiable.
(ii) For all F, F is valid or ~F is valid.
How do I prove which is true and which is false?
Statement (i) is true, as for all F, F will either be satisfiable, or ~F will be satisfiable (truth table). However, how do I go about solving for statement (ii)?
Any help is highly appreciated!