∀ {α : Type u_4} {β : Type u_5} {mα : MeasurableSpace α} {mβ : MeasurableSpace β} {μ ν : MeasureTheory.Measure (α × β)}
  [MeasureTheory.IsFiniteMeasure μ],
  (∀ {s : Set α} {t : Set β}, MeasurableSet s → MeasurableSet t → μ (s ×ˢ t) = ν (s ×ˢ t)) → μ = ν