fix(03): fix natural deduction proof
fix(03): fix natural deduction proof

avigad/logic_and_proof,fpvandoorn/logic_and_proof,leanprover/logic_and_proof,avigad/logic_and_proof,leanprover/logic_and_proof,avigad/logic_and_proof,fpvandoorn/logic_and_proof,rlewis1988/logic_and_proof,rlewis1988/logic_and_proof,soonhokong/logic_and_proof,rlewis1988/logic_and_proof,leanprover/logic_and_proof,soonhokong/logic_and_proof,soonhokong/logic_and_proof,fpvandoorn/logic_and_proof