simp only [isFreeIn]
case h1.h2
P Q : Formula
v : VarName
h1 : ¬isFreeIn v P
⊢ ¬isFreeIn v (P.imp_ (forall_ v Q))
case h1.h2
P Q : Formula
v : VarName
h1 : ¬isFreeIn v P
⊢ ¬(isFreeIn v P ∨ ¬True ∧ isFreeIn v Q)