Finite-horizon conservation and comprehensive valuation: comprehensive finite valuation
ProvedActuarialFoundations.fa_comprehensive_finite_valuationactuarial-scienceformal-verificationlife-table-commutation
The comprehensive finite-cohort valuation theorem combines the original 15-conclusion whole-life foundation with the new finite-term family. Its hypotheses do not assume an annuity or assurance relationship, and its proof must derive both prerequisite capstones.
Preamble
import Mathlib.Data.Real.Basic import Mathlib.Algebra.BigOperators.Group.Finset.Basic import Mathlib.Analysis.SpecialFunctions.Exp import Mathlib.Analysis.SpecialFunctions.Log.Basic import Definitions.Def_actuarial_faAnnuityArrearsOriginal import Definitions.Def_actuarial_faAnnuityOriginal import Definitions.Def_actuarial_faAssuranceOriginal import Definitions.Def_actuarial_faDeaths import Definitions.Def_actuarial_faDeferredAnnuityOriginal import Definitions.Def_actuarial_faDeferredAssuranceOriginal import Definitions.Def_actuarial_faDeferredMortality import Definitions.Def_actuarial_faDiscountedDeaths import Definitions.Def_actuarial_faDiscountedLives import Definitions.Def_actuarial_faEndowmentAssuranceOriginal import Definitions.Def_actuarial_faFiniteCohortValid import Definitions.Def_actuarial_faIncreasingAnnuityOriginal import Definitions.Def_actuarial_faIncreasingAssuranceOriginal import Definitions.Def_actuarial_faIncreasingTemporaryAnnuityOriginal import Definitions.Def_actuarial_faIncreasingTermAssuranceOriginal import Definitions.Def_actuarial_faM import Definitions.Def_actuarial_faMultiYearMortality import Definitions.Def_actuarial_faN import Definitions.Def_actuarial_faOneYearMortality import Definitions.Def_actuarial_faPureEndowmentOriginal import Definitions.Def_actuarial_faR import Definitions.Def_actuarial_faRAbsolute import Definitions.Def_actuarial_faS import Definitions.Def_actuarial_faSurvival import Definitions.Def_actuarial_faTemporaryAnnuityOriginal import Definitions.Def_actuarial_faTermAssuranceOriginal
Formal statement
namespace ActuarialFoundations theorem fa_comprehensive_finite_valuation (l : ℕ → ℝ) (v : ℝ) (ω x : ℕ) (h : faFiniteCohortValid l ω) (hx : x < ω) (hp : 0 < l x) (hv : 0 < v) (hv1 : v ≤ 1) : ((faSurvival l x 0 = 1) ∧ (faSurvival l x (ω-x) = 0) ∧ (∀ n, x+n ≤ ω → 0 ≤ faSurvival l x n ∧ faSurvival l x n ≤ 1) ∧ ((∑ k ∈ Finset.range (ω-x), faDeaths l (x+k) / l x) = 1) ∧ ((∑ k ∈ Finset.range (ω-x), faDeaths l (x+k)) = l x) ∧ (faAnnuityOriginal l v ω x = faN l v ω x / faDiscountedLives l v x) ∧ (faAssuranceOriginal l v ω x = faM l v ω x / faDiscountedLives l v x) ∧ (faN l v ω x = faDiscountedLives l v x + faN l v ω (x+1)) ∧ (faM l v ω x = faDiscountedDeaths l v x + faM l v ω (x+1)) ∧ (faS l v ω x = faN l v ω x + faS l v ω (x+1)) ∧ (faR l v ω x = faM l v ω x + faR l v ω (x+1)) ∧ (faIncreasingAnnuityOriginal l v ω x = faS l v ω x / faDiscountedLives l v x) ∧ (faIncreasingAssuranceOriginal l v ω x = faR l v ω x / faDiscountedLives l v x) ∧ (faRAbsolute l v ω x = faR l v ω x + (x : ℝ) * faM l v ω x) ∧ (faAssuranceOriginal l v ω x + (1-v)*faAnnuityOriginal l v ω x = 1)) ∧ ((faOneYearMortality l x + faSurvival l x 1 = 1) ∧ (faAnnuityArrearsOriginal l v ω x = (faN l v ω x - faDiscountedLives l v x) / faDiscountedLives l v x) ∧ (faM l v ω x + (1-v) * faN l v ω x = faDiscountedLives l v x) ∧ (∀ n : ℕ, x+n ≤ ω → (faMultiYearMortality l x n + faSurvival l x n = 1) ∧ (faPureEndowmentOriginal l v x n = faDiscountedLives l v (x+n) / faDiscountedLives l v x) ∧ (faTemporaryAnnuityOriginal l v x n = (faN l v ω x - faN l v ω (x+n)) / faDiscountedLives l v x) ∧ (faTermAssuranceOriginal l v x n = (faM l v ω x - faM l v ω (x+n)) / faDiscountedLives l v x) ∧ (faEndowmentAssuranceOriginal l v x n = (faM l v ω x - faM l v ω (x+n) + faDiscountedLives l v (x+n)) / faDiscountedLives l v x) ∧ (faIncreasingTemporaryAnnuityOriginal l v x n = (faS l v ω x - faS l v ω (x+n) - (n : ℝ) * faN l v ω (x+n)) / faDiscountedLives l v x) ∧ (faIncreasingTermAssuranceOriginal l v x n = (faR l v ω x - faR l v ω (x+n) - (n : ℝ) * faM l v ω (x+n)) / faDiscountedLives l v x) ∧ ((faM l v ω x - faM l v ω (x+n)) + (1-v) * (faN l v ω x - faN l v ω (x+n)) + faDiscountedLives l v (x+n) = faDiscountedLives l v x) ∧ (faDeferredAnnuityOriginal l v ω x n = faN l v ω (x+n) / faDiscountedLives l v x) ∧ (faDeferredAssuranceOriginal l v ω x n = faM l v ω (x+n) / faDiscountedLives l v x) ∧ (∀ t : ℕ, x+n+t ≤ ω → 0 ≤ faSurvival l x (n+t) ∧ faSurvival l x (n+t) ≤ faSurvival l x n ∧ faSurvival l x n ≤ 1) ∧ (∀ t : ℕ, x+n+t ≤ ω → 0 < l (x+n) → faSurvival l x (n+t) = faSurvival l x n * faSurvival l (x+n) t ∧ faDeferredMortality l x n t = faSurvival l x n * faMultiYearMortality l (x+n) t) ∧ (∀ t r : ℕ, x+n+t+r ≤ ω → faDeferredMortality l x n t + faDeferredMortality l x (n+t) r = faDeferredMortality l x n (t+r)))) := by sorry end ActuarialFoundations
Source
Institute of Actuaries (1969–1971), International Actuarial Notation, commutation and assurance-annuity relations; https://www.actuaries.org.uk/system/files/documents/pdf/0042-0071.pdf Original-derived finite-cohort Lean statement; this exact theorem wording is not attributed to the text.
Human review
Confirmed by the mission captain (proposal self-audit).
Confirmed by the moderator at approval.