try first
| apply verum!;
| apply imply₁!;
| apply imply₂!;
| apply conj₁!;
| apply conj₂!;
| apply conj₃!;
| apply disj₁!;
| apply disj₂!;
| apply disj₃!;
| apply dne!;
case mp.hDne
α : Type u_1
inst✝ : DecidableEq α
p p✝ : Formula α
h : 𝐕𝐞𝐫 ⊢! ~~p✝ ⟶ p✝
⊢ 𝐂𝐥 ⊢! (((p✝ⱽᴾ) ⋯ ⟶ ⊥) ⟶ ⊥) ⟶ (p✝ⱽᴾ) ⋯
no goals