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

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