∀ {G : Type u_1} {α : Type u_3} [inst : AddGroup G] [inst_1 : AddAction G α] [inst_2 : MeasurableSpace α] {s : Set α}
  {μ : MeasureTheory.Measure α} [MeasurableConstVAdd G α] [MeasureTheory.VAddInvariantMeasure G α μ] [Countable G]
  {ν : MeasureTheory.Measure α},
  MeasureTheory.IsAddFundamentalDomain G s μ →
    ν.AbsolutelyContinuous μ → ∀ (t : Set α), ν t = ∑' (g : G), ν (t ∩ (g +ᵥ s))