I know there are some that can be proven, but I wonder if there are exceptions?


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    $\begingroup$ If a conjunctive normal form has a clause consisting of a single literal, then it's not a tautology, so it can't be proved (by natural deduction or any other correct method). $\endgroup$ – Andreas Blass Jan 13 at 19:55
  • $\begingroup$ This question shouldn't have been closed without giving you a chance to edit and clarify the meaning. You can still edit, though, and then the question can be reopened if Andreas's comment doesn't answer it. $\endgroup$ – Will Sawin Jan 16 at 20:22

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