∀ {α : Type u_1} {β : Type u_2} {γ : Type u_3} {mα : MeasurableSpace α} {mβ : MeasurableSpace β}
  {mγ : MeasurableSpace γ} (η : ProbabilityTheory.Kernel β γ) (κ : ProbabilityTheory.Kernel α β) (a : α),
  (η.comp κ) a = (κ a).bind ⇑η