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First-contraction quarter gap from a supplied numerical certificate

Proved
CollatzWork.firstContraction_quarter_of_certificate

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 qk(n)q_k(n)qk​(n) count the odd inputs among the first kkk shortcut steps, and let R0(n)=0R_0(n)=0R0​(n)=0; recursively Rk+1(n)=Rk(n)R_{k+1}(n)=R_k(n)Rk+1​(n)=Rk​(n) for an even input Tk(n)T^k(n)Tk(n) and Rk+1(n)=3Rk(n)+2kR_{k+1}(n)=3R_k(n)+2^kRk+1​(n)=3Rk​(n)+2k for an odd input. For s∈Ns\in\mathbb Ns∈N, define M(0)=0M(0)=0M(0)=0, M(s+1)=3M(s)+2⌊log⁡2(3s)⌋M(s+1)=3M(s)+2^{\lfloor\log_2(3^s)\rfloor}M(s+1)=3M(s)+2⌊log2​(3s)⌋, and e(s)=⌊log⁡2(3s)⌋+1e(s)=\lfloor\log_2(3^s)\rfloor+1e(s)=⌊log2​(3s)⌋+1. A first coefficient contraction at time kkk means k>0k>0k>0, 3qk(n)<2k3^{q_k(n)}<2^k3qk​(n)<2k, and 2j≤3qj(n)2^j\le3^{q_j(n)}2j≤3qj​(n) for every j<kj<kj<k. Its existence is a hypothesis.

Let n,k,d∈Nn,k,d\in\mathbb Nn,k,d∈N, n>0n>0n>0, with a first coefficient contraction at kkk and Tk(n)=n+dT^k(n)=n+dTk(n)=n+d. Assume 4M(qk(n))≤qk(n)2e(qk(n))4M(q_k(n))\le q_k(n)2^{e(q_k(n))}4M(qk​(n))≤qk​(n)2e(qk​(n)). Then

4d<qk(n).4d<q_k(n).4d<qk​(n).

This isolates the exact numerical certificate needed by the orbit argument.

Preamble
import Std
import Init.Grind.Ordered.Module
import Definitions.Def_CollatzWork_ConvergenceStatement
import Definitions.Def_CollatzWork_QuarterGapStatement
import Theorems.Thm_CollatzWork_orbitAffine
import Theorems.Thm_CollatzWork_mechanicalEnvelope
import Theorems.Thm_CollatzWork_affineQuarterCertificate



Formal statement
theorem CollatzWork.firstContraction_quarter_of_certificate {n k d : Nat}
    (hn : 0 < n) (hfirst : FirstCoefficientContraction n k)
    (hreturn : shortcutIter k n = n + d)
    (hcert : 4 * mechanicalMax (orbitOddCount n k) ≤
      orbitOddCount n k * 2 ^ coefficientCrossingExponent (orbitOddCount n k)) :
    4 * d < orbitOddCount n k := by sorry

Source
https://github.com/Sodelin/Collatz-Conjecture-Work/blob/026aa4ad4be6453a005ab950b160a9f2204c5271/lean/CollatzWork/QuarterGap.lean#L94-L116

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