English
For f integrable on s ∪ t with μ, f is integrable on s and on t; conversely, integrability on s and on t implies integrability on s ∪ t.
Русский
Для интегрируемости f на s ∪ t по μ эквивалентно интегрируемости на s и на t по μ, и обратно.
LaTeX
$$$\mathrm{IntegrableOn}(f,s\cup t,\mu) \iff \mathrm{IntegrableOn}(f,s,\mu) \land \mathrm{IntegrableOn}(f,t,\mu)$$$
Lean4
@[simp]
theorem integrableOn_union [PseudoMetrizableSpace ε] :
IntegrableOn f (s ∪ t) μ ↔ IntegrableOn f s μ ∧ IntegrableOn f t μ :=
⟨fun h => ⟨h.left_of_union, h.right_of_union⟩, fun h => h.1.union h.2⟩