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

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