A Counterexample to Ziegler's Cross-Polytope Conjecture for Simplicial 0/1-Polytopes

Volker Kaibel, Sebastian Pokutta

Fourteen binary vertices form a simplicial seven-dimensional 0/1-polytope with the maximum 2d vertices but without central symmetry, countering the proposed cross-polytope characterization.

Sources for this record

What was already known

Ziegler proved the 2d vertex bound. Prior enumeration supported the characterization through dimension six.

AI involvement AI-centered

A DeepSeek V4 Flash/GLM 5.2 agent found the antipodal split structure that led to the witness. Kaibel and Pokutta verified and explained the final construction.

The agent supplied the retained antipodal-structure insight leading to the witness; Kaibel and Pokutta framed, checked and wrote the final result.

Importance Notable

Provides a counterexample in the first possible dimension.

Limitations

Two independent exact-rational computations check the explicit witness; the separate enumeration of five symmetry classes is not part of this claim. An earlier failed Lean proof did not check the counterexample.

Technical verification Formal (two exact rational polytope computations, including polymake SIMPLICIAL)

For this finite explicit witness, the paper reports two independent exact-rational computations of all load-bearing polytope properties, with agreement. The source-reported exact certificate covers the counterexample; the broader five-class enumeration is a separate claim.

Formal checking

Two independent exact-rational implementations check the explicit witness’s dimension, facets, simpliciality and lack of central symmetry.

Checker
Two independent exact-rational implementations reported by Kaibel and Pokutta
Scope
The fourteen listed 0/1 vertices form a full-dimensional simplicial seven-polytope with 136 facets and without central symmetry
Basis
Reported by the linked checker
Evidence source

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

Human understanding Full

The named authors explain the balanced-coordinate and split-pair reduction that led to the example, and give a direct geometric account of its missing antipodes and simpliciality.

Correction and publication history