Kourovka Problem 21.147: Non-abelian counterexample for relatively convex subgroups

In a non-abelian right-orderable group, the right-relatively convex subgroups need not form a sublattice of its subgroup lattice.

Sources for this record

What was already known

An abelian counterexample was already known; the problem authors clarified that the intended question asked for a non-abelian one.

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

Aristotle’s revised construction supplies a non-abelian counterexample to the intended question.

Limitations

The initial abelian example was already known. The contribution assessed here is the later non-abelian construction after the authors’ clarification.

Technical verification Formal (Lean 4)

The companion metadata names declaration kourovka_21_147 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_147.

Checker
Lean 4
Scope
In a non-abelian right-orderable group, the right-relatively convex subgroups need not form a sublattice of its subgroup lattice.
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