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Finite-horizon conservation and comprehensive valuation: comprehensive finite valuation

Proved
ActuarialFoundations.fa_comprehensive_finite_valuation

by WillR · Oct 11, 2026 · Mathlib 0df444a (Lean v4.33.1)

actuarial-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
  • Endorsed by Shuze Chen · Oct 11, 2026

    Confirmed by the moderator at approval.

  • Endorsed by WillR · Oct 11, 2026

    Confirmed by the mission captain (proposal self-audit).

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