cases h2
v u x y : VarName
binders : Finset VarName
h1 : v ∉ binders
h2 : (x ∈ binders ↔ (if v = x then u else x) ∈ binders) ∧ (y ∈ binders ↔ (if v = y then u else y) ∈ binders)
⊢ v = x ∨ v = y → u ∉ binders
case intro
v u x y : VarName
binders : Finset VarName
h1 : v ∉ binders
left✝ : x ∈ binders ↔ (if v = x then u else x) ∈ binders
right✝ : y ∈ binders ↔ (if v = y then u else y) ∈ binders
⊢ v = x ∨ v = y → u ∉ binders