Kourovka Problem 21.8: Class transpositions generate the full symmetric group

For k ≥ 4, horizontal class transpositions of moduli at most k generate a group isomorphic to the symmetric group on lcm(2,…,k) letters.

Sources for this record

What was already known

Bardakov and Iskra conjectured this general description after studying class transpositions for particular moduli.

AI involvement AI-autonomous

Van Doorn, Judin, Monticone and Morrison report that Aristotle developed the proof strategy and Lean proof without human guidance on mathematical steps. The authors chose problems, supplied infrastructure, refined the formal code, translated the proofs into prose and arranged external review.

The authors say Aristotle developed the new mathematical argument and formal proof strategy without human guidance on the mathematical steps. Humans selected the task, supplied infrastructure, refined the code and wrote the prose account.

Importance Modest

The proof gives a general group description for Problem 21.8.

Limitations

Pan independently proved the same result; this record credits Aristotle’s separate proof and Lean formalization, not priority over Pan.

Technical verification Formal (Lean 4)

The companion metadata names declaration kourovka_21_8 and reports a complete Lean proof with zero sorry. This is a source-reported machine check of the scoped theorem; the assessment did not compile the project.

Formal checking

The authors report a Lean 4 proof with zero sorry for declaration kourovka_21_8.

Checker
Lean 4
Scope
For k ≥ 4, horizontal class transpositions of moduli at most k generate a group isomorphic to the symmetric group on lcm(2,…,k) letters.
Basis
Reported by the linked checker
Evidence source

Checking a formal statement does not establish that it matches the original problem.

Human understanding Full

Van Doorn, Judin, Monticone and Morrison translated the formal solution, refined the explanation and present the construction or proof in mathematical prose. This documents human explanation of the central argument.

Correction and publication history

2026-10-18 · publication

Primary-source review of the scoped Kourovka result, AI contribution, Lean checking, human prose proof and prior baseline. Historical, non-notifying addition.

Read this published revision