∀ {ι : Type u_1} {f : ι → ℝ} (x : ℝ) (motive : (x ∈ Set.range fun s => ∑ b ∈ s, f b) → Prop)
  (x_1 : x ∈ Set.range fun s => ∑ b ∈ s, f b),
  (∀ (u : Finset ι) (hu : (fun s => ∑ b ∈ s, f b) u = x), motive ⋯) → motive x_1