English
Let ρ be a finite measure on α × ℝ and r rational. Then the integral of (preCDF ρ r a)^{toReal} over the whole α with respect to ρ_fst equals the real part of ρ(IicSnd r.cast) over univ, i.e., (ρ.IicSnd r.cast).real univ.
Русский
Пусть ρ — конечная мера на α × ℝ и r рационально. Тогда интеграл по всей α функции (preCDF ρ r a)^{toReal} по мере ρ_fst равен вещественной мере множества (-∞, r] в пространстве α × ℝ, то есть (ρ.IicSnd r.cast).real univ.
LaTeX
$$$\\int_{a} (\\mathrm{preCDF}(ρ,r,a))^{\\mathrm{toReal}} dρ_{\\\\mathrm fst}(a) = (ρ.IicSnd(r.cast)).real(\\\\mathrm{univ}).$$
Lean4
theorem integral_preCDF_fst (ρ : Measure (α × ℝ)) (r : ℚ) [IsFiniteMeasure ρ] :
∫ x, (preCDF ρ r x).toReal ∂ρ.fst = (ρ.IicSnd r).real univ := by
rw [← setIntegral_univ, setIntegral_preCDF_fst ρ _ MeasurableSet.univ]