⊢φ→(((ψ→φ)→δ)→δ)

Question

I solved this exercice but I don't know if it's correct. The solution is on the following image:

solution

Answer 1

Almost. Line 4 should instead be a repeat of $\phi$ (you should have a repeat rule; otherwise you need to pull an ugly trick like introducing $\phi \land \phi$ and then elimiting the conjunction again). Then, on line 5, you should conclude the subproof that started with introducing $\psi$ and derive $\psi \to \phi$. Then, your proof continues as you have written it.