cases v
case h
D : Type
V : VarAssignment D
v : Var
⊢ V (Var.openList 0 [] v) = V v
case h.free_
D : Type
V : VarAssignment D
a✝ : String
⊢ V (Var.openList 0 [] (free_ a✝)) = V (free_ a✝)

case h.bound_
D : Type
V : VarAssignment D
a✝ : ℕ
⊢ V (Var.openList 0 [] (bound_ a✝)) = V (bound_ a✝)