apply IsReplOfFormulaInFormula.diff_
case h1.a.a
P Q : Formula
v : VarName
h1 : ¬isFreeIn v P
⊢ IsReplOfFormulaInFormula (forall_ v P) P (forall_ v P) P
case h1.a.a.a
P Q : Formula
v : VarName
h1 : ¬isFreeIn v P
⊢ forall_ v P = forall_ v P

case h1.a.a.a
P Q : Formula
v : VarName
h1 : ¬isFreeIn v P
⊢ P = P