I want to prove double negation introduction in sequent calculus using the most basic rule set.
That is what I want to prove: from the sequent $$\Gamma \rightarrow\Phi,$$ the sequent $$\Gamma \rightarrow\neg\neg\Phi$$ is derivable.
How is this accomplished? It's seems much more difficult than in natural deduction. I think I may be able to prove the conjunction myself once I have this result.