apply IsDeduct.mp_ (forall_ v P)
P : Formula
v t : VarName
Δ : Set Formula
h1 : IsDeduct Δ (forall_ v P)
h2 : fastAdmits v t P
⊢ IsDeduct Δ (fastReplaceFree v t P)
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
P : Formula
v t : VarName
Δ : Set Formula
h1 : IsDeduct Δ (forall_ v P)
h2 : fastAdmits v t P
⊢ IsDeduct Δ (forall_ v P)