apply IsDeduct.axiom_
case a
P : Formula
v t : VarName
Δ : Set Formula
h1 : IsDeduct Δ (forall_ v P)
h2 : fastAdmits v t P
⊢ IsDeduct Δ ((forall_ v P).imp_ (fastReplaceFree v t P))
case a.a
P : Formula
v t : VarName
Δ : Set Formula
h1 : IsDeduct Δ (forall_ v P)
h2 : fastAdmits v t P
⊢ IsAxiom ((forall_ v P).imp_ (fastReplaceFree v t P))