Kourovka Problem 20.125: A surjective non-injective Rota–Baxter operator on a non-abelian group

A non-abelian group admits a weight-one Rota–Baxter operator that is surjective but not injective, answering Problem 20.125.

Sources for this record

What was already known

The existence of a surjective, non-injective operator of this kind on a non-abelian group was an open question of Bardakov and Gubarev.

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 construction resolves that specific existence question.

Limitations

It is an existence example, not a classification of Rota–Baxter operators on groups.

Technical verification Formal (Lean 4)

The companion metadata names declaration kourovka_20_125 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_20_125.

Checker
Lean 4
Scope
A non-abelian group admits a weight-one Rota–Baxter operator that is surjective but not injective, answering Problem 20.125.
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.

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