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

case a
P : Formula
v t : VarName
Δ : Set Formula
h1 : fastAdmits v t P
h2 : IsDeduct Δ (fastReplaceFree v t P)
⊢ IsDeduct Δ (fastReplaceFree v t P)