apply generalization
case h1.a
P Q : Formula
v : VarName
⊢ IsDeduct {forall_ v (P.iff_ Q)} (forall_ v (Q.iff_ P))
case h1.a.h1
P Q : Formula
v : VarName
⊢ IsDeduct {forall_ v (P.iff_ Q)} (Q.iff_ P)

case h1.a.h2
P Q : Formula
v : VarName
⊢ ∀ H ∈ {forall_ v (P.iff_ Q)}, ¬isFreeIn v H