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