apply IsDeduct.assume_
case h1.a.a.a.h1.a.h1
P Q : Formula
v : VarName
h1 : ¬isFreeIn v Q
⊢ IsDeduct {forall_ v (P.imp_ Q)} (forall_ v (P.imp_ Q))
case h1.a.a.a.h1.a.h1.a
P Q : Formula
v : VarName
h1 : ¬isFreeIn v Q
⊢ forall_ v (P.imp_ Q) ∈ {forall_ v (P.imp_ Q)}