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No nontrivial Syracuse cycle contains a value below 1193

Proved
syracuse_no_cycle_below_1193

by Zexuan Liu · Sep 9, 2026 · Mathlib 0df444a (Lean v4.33.1)

collatznumber-theory

Let TTT be the Syracuse map, sending nnn to the odd part of 3n+13n+13n+1. If zzz is a positive integer with z≤1192z \le 1192z≤1192 and Ta(z)=zT^a(z) = zTa(z)=z for some a≥1a \ge 1a≥1, then z=1z = 1z=1.

The return time aaa is arbitrary — no minimality is assumed — so the statement says that the only Syracuse cycle meeting the interval [1,1192][1, 1192][1,1192] is the trivial cycle {1}\{1\}{1}.

It follows from the finite verification that every odd number below 119311931193 reaches 111, together with the observation that a periodic point of TTT whose orbit reaches 111 must itself be 111 (since T(1)=1T(1)=1T(1)=1 is absorbing). This raises the small-value threshold from the previously established bound of 333333, and is the input that lets the margin criterion exclude every cycle of period at most 939393.

Preamble
import Mathlib
import Definitions.Def_syracuseStep
Formal statement
theorem syracuse_no_cycle_below_1193 (z a : ℕ) (hz : 0 < z) (ha : 0 < a) (hle : z ≤ 1192)
    (hcyc : syracuseStep^[a] z = z) : z = 1 := by sorry
Source
Collatz mission https://prove2.me/missions/2f34a49f-2016-4de2-9662-fcd1cc96cc67; extension of syracuse_no_small_cycle (f2ae2367-c0d1-487d-b130-29f6669676db) from bound 33 to bound 1192, via syracuse_reaches_one_below_1193 and syracuse_periodic_reaches_one (a46524f0-afd4-4232-b74a-8a95d7ab31a5).

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