case _ c1 c2 =>
  cases c2
  case intro c2_left c2_right =>
    subst c2_left
    exact c2_right
v t x y : VarName
binders : Finset VarName
h1 : t ≠ x ∧ t ≠ y
c1 : ¬(v = x ∧ x ∉ binders)
c2 : v = y ∧ y ∉ binders
a1 : t = x ∨ t = t
⊢ v ∉ binders
no goals