apply IsDeduct.axiom_
F : Formula
Δ Γ : Set Formula
h1_phi : Formula
h1_1 : IsAxiom h1_phi
⊢ IsDeduct (Δ ∪ Γ) h1_phi
case a
F : Formula
Δ Γ : Set Formula
h1_phi : Formula
h1_1 : IsAxiom h1_phi
⊢ IsAxiom h1_phi