simp only [def_iff_]
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.imp_ Q).and_ (Q.imp_ P))} (((P.imp_ Q).and_ (Q.imp_ P)).imp_ ((Q.imp_ P).and_ (P.imp_ Q)))