exact h1_ih_2
case a
F : Formula
Δ Γ : Set Formula
h1_phi h1_psi : Formula
a✝¹ : IsDeduct Δ (h1_phi.imp_ h1_psi)
a✝ : IsDeduct Δ h1_phi
h1_ih_1 : IsDeduct (Δ ∪ Γ) (h1_phi.imp_ h1_psi)
h1_ih_2 : IsDeduct (Δ ∪ Γ) h1_phi
⊢ IsDeduct (Δ ∪ Γ) h1_phi
no goals