apply deduction_theorem
P Q : Formula
v : VarName
h1 : ¬isFreeIn v Q
⊢ IsProof ((forall_ v (P.imp_ Q)).imp_ ((exists_ v P).imp_ Q))
case h1
P Q : Formula
v : VarName
h1 : ¬isFreeIn v Q
⊢ IsDeduct (∅ ∪ {forall_ v (P.imp_ Q)}) ((exists_ v P).imp_ Q)