Kourovka Problem 21.24: Finite-group cograph power graphs are chordal

Every power graph of a finite group that is a cograph is chordal; equivalently, an induced four-cycle forces an induced four-vertex path.

Sources for this record

What was already known

The corresponding implication was known for enhanced power graphs, while the ordinary power-graph case was posed as Problem 21.24.

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 settles the finite-group power-graph implication.

Limitations

Rundström independently solved this problem and is separately credited by the Notebook; this record covers Aristotle’s proof.

Technical verification Formal (Lean 4)

The companion metadata names declaration kourovka_21_24 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_24.

Checker
Lean 4
Scope
Every power graph of a finite group that is a cograph is chordal; equivalently, an induced four-cycle forces an induced four-vertex path.
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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