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Product envelope for an arbitrary finite segment list

Proved
CollatzWork.excursionChainEnvelope

by Sodelin · Sep 8, 2026 · Mathlib 0df444a (Lean v4.33.1)

collatz-work-import

Let T:N→NT:\mathbb N\to\mathbb NT:N→N be the shortcut Collatz map: T(n)=n/2T(n)=n/2T(n)=n/2 for even nnn and T(n)=(3n+1)/2T(n)=(3n+1)/2T(n)=(3n+1)/2 for odd nnn. Write TkT^kTk for its kkk-fold iterate, with T0(n)=nT^0(n)=nT0(n)=n. Let SSS be a finite list of segments (ki,Ai,Di)(k_i,A_i,D_i)(ki​,Ai​,Di​) of natural numbers, with Di>0D_i>0Di​>0. Starting from nnn, define successive endpoints by applying TkiT^{k_i}Tki​. Assume each segment satisfies Di(endpoint+3)≤Ai(start+3)D_i(\text{endpoint}+3)\le A_i(\text{start}+3)Di​(endpoint+3)≤Ai​(start+3). Write K=∑ikiK=\sum_i k_iK=∑i​ki​, A=∏iAiA=\prod_i A_iA=∏i​Ai​, and D=∏iDiD=\prod_i D_iD=∏i​Di​, with empty products 1.

Under the segment assumptions,

D(TK(n)+3)≤A(n+3),D>0.D(T^K(n)+3)\le A(n+3),\qquad D>0.D(TK(n)+3)≤A(n+3),D>0.

The list can have any finite length, including zero. All segment inequalities remain explicit premises.

Preamble
import Std
import Init.Grind.Ordered.Module
import Definitions.Def_CollatzWork_ConvergenceStatement
import Definitions.Def_CollatzWork_ExcursionBudgetStatement
import Theorems.Thm_CollatzWork_shiftedEnvelope_compose



Formal statement
theorem CollatzWork.excursionChainEnvelope : ExcursionChainEnvelopeStatement := by sorry

Source
https://github.com/Sodelin/Collatz-Conjecture-Work/blob/026aa4ad4be6453a005ab950b160a9f2204c5271/lean/CollatzWork/ExcursionBudget.lean#L28-L43

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