∀ {α : Type u_1} (a : Batteries.RBNode α) (x : α) (b c : Batteries.RBNode α) (y : α) (d : Batteries.RBNode α),
  InvImage (fun x1 x2 => x1 < x2) (fun x => PSigma.casesOn x fun a a_1 => a.size + a_1.size) ⟨b, c⟩
    ⟨Batteries.RBNode.node Batteries.RBColor.black a x b, Batteries.RBNode.node Batteries.RBColor.black c y d⟩