case eq_ x y =>
  push_neg at h1
  intros a1
  split_ifs at a1
  case _ c1 c2 =>
    cases c1
    case intro c1_left c1_right =>
      subst c1_left
      exact c1_right
  case _ c1 c2 =>
    cases c1
    case intro c1_left c1_right =>
      subst c1_left
      exact c1_right
  case _ c1 c2 =>
    cases c2
    case intro c2_left c2_right =>
      subst c2_left
      exact c2_right
  case _ c1 c2 =>
    tauto
v t x y : VarName
binders : Finset VarName
h1 : ¬(t = x ∨ t = y)
⊢ ((t = if v = x ∧ x ∉ binders then t else x) ∨ t = if v = y ∧ y ∉ binders then t else y) → v ∉ binders
no goals