∀ {α : Type u_1} (a : Lists α) (b : Bool) (b_1 : Lists' α b) (l₂ : Lists' α true),
  sizeOf ⟨b, b_1⟩ < 1 + 1 + sizeOf b_1 + sizeOf l₂ →
    InvImage (fun x1 x2 => x1 < x2)
      (fun x =>
        PSum.casesOn x (fun _x => PSigma.casesOn _x fun l₁ l₂ => sizeOf l₁ + sizeOf l₂) fun _x =>
          PSum.casesOn _x (fun _x => PSigma.casesOn _x fun l₁ l₂ => sizeOf l₁ + sizeOf l₂) fun _x =>
            PSigma.casesOn _x fun a l => sizeOf a + sizeOf l)
      (PSum.inl ⟨a, ⟨b, b_1⟩⟩) (PSum.inr (PSum.inr ⟨a, b_1.cons' l₂⟩))