apply T_18_2 U V P_U P_V ((U.freeVarSet ∪ V.freeVarSet) ∩ P_U.boundVarSet).toList h1
case a
U V P_U P_V : Formula
h1 : IsReplOfFormulaInFormula U V P_U P_V
h2 : IsProof (U.iff_ V)
⊢ IsDeduct ∅ ((Forall_ ((U.freeVarSet ∪ V.freeVarSet) ∩ P_U.boundVarSet).toList (U.iff_ V)).imp_ (P_U.iff_ P_V))
case a
U V P_U P_V : Formula
h1 : IsReplOfFormulaInFormula U V P_U P_V
h2 : IsProof (U.iff_ V)
⊢ ∀ (v : VarName),
    (isFreeIn v U ∨ isFreeIn v V) ∧ isBoundIn v P_U → v ∈ ((U.freeVarSet ∪ V.freeVarSet) ∩ P_U.boundVarSet).toList