Panjer frequency recursion and zero-size correction: pgCountSupport_zero
ProvedActuarialValuation.pgCountSupport_zeroactuarial-scienceformal-verificationgeneral-finite-panjer
A zero-horizon count model is concentrated at no claims. The exact assumptions, units and boundary conventions are recorded separately in the formal statement.
Mathematical relation:
Preamble
import Mathlib.Data.Real.Basic import Mathlib.Algebra.BigOperators.Group.Finset.Basic import Definitions.Def_actuarial_pgCountSupport
Formal statement
namespace ActuarialValuation theorem pgCountSupport_zero (p : ℕ → ℝ) (h : pgCountSupport p 0) (n : ℕ) (hn : n≠0) : p n=0 := by sorry end ActuarialValuation
Source
Original derived actuarial mathematics, published source page 397. Harry H. Panjer, Recursive Evaluation of a Family of Compound Distributions (1981), https://doi.org/10.1017/S0515036100006796; Sundt and Jewell (1981), Further Results on Recursive Evaluation of Compound Distributions, https://doi.org/10.1017/S0515036100006802; S. D. Promislow, Fundamentals of Actuarial Mathematics (2015), chapter 21. Parent topic: Finite-support Panjer counting law, severity convolution powers, aggregate distribution by genuine random-sum weights and corrected zero-severity Panjer recurrence. The particular Lean formula is a new finite/real-algebraic formalisation and remains an unproved theorem target if labelled theorem. Relevant published actuarial derivation: https://www.cambridge.org/core/journals/astin-bulletin-journal-of-the-iaa/article/recursive-evaluation-of-a-family-of-compound-distributions/BD6628F3853600A8F79C6A45E92938CB
Human review
Confirmed by the mission captain (proposal self-audit).
Confirmed by the moderator at approval.