case _ c1 =>
  simp only [Finset.mem_union] at c1
  push_neg at c1
  cases c1
  case _ c1_left c1_right =>
    have s1 : ¬ v = x
    intro contra
    apply c1_right
    subst contra
    exact a1
    simp only [Function.updateITE]
    simp only [if_neg s1]
    exact h2 v a1
D : Type
I : Interpretation D
V'' : VarAssignment D
E : Env
c : Char
τ : PredName → ℕ → Option (List VarName × Formula)
x : VarName
phi : Formula
ih :
  ∀ (V V' : VarAssignment D) (σ : VarName → VarName),
    (∀ (x : VarName), isFreeIn x phi → V' x = V (σ x)) →
      (∀ x ∈ phi.predVarSet.biUnion (predVarFreeVarSet τ), V'' x = V x) →
        (Holds D (I' D I V'' E τ) V' E phi ↔ Holds D I V E (subAux c τ σ phi))
V V' : VarAssignment D
σ : VarName → VarName
h1 : ∀ (x_1 : VarName), ¬x_1 = x ∧ isFreeIn x_1 phi → V' x_1 = V (σ x_1)
h2 : ∀ x ∈ phi.predVarSet.biUnion (predVarFreeVarSet τ), V'' x = V x
d : D
v : VarName
a1 : v ∈ phi.predVarSet.biUnion (predVarFreeVarSet τ)
c1 : x ∉ Finset.image (Function.updateITE σ x x) phi.freeVarSet ∪ phi.predVarSet.biUnion (predVarFreeVarSet τ)
⊢ V'' v = Function.updateITE V x d v
no goals