An indecomposable equiprojective polytope with eleven vertices

Buffière and Pournin asked whether a convex three-dimensional polytope can be both equiprojective and Minkowski indecomposable. We answer affirmatively with an eleven-vertex polytope whose coordinates belong to {−1, 0, 1}. Every orthogonal projection in a direction parallel to no facet is a heptagon. Its six triangular facets occur in translated pairs, and its six remaining facets are parallelograms; these features give a complete compensation pairing. Requiring edge vectors to close around these faces forces every Minkowski summand to be a translated scaled copy of the whole polytope. We describe the direct search route, give the exact geometry and elementary proofs, and supply a standalone Python verifier using rational arithmetic.

Authors

Publication Details

Journal
Zenodo (CERN European Organization for Nuclear Research)
Published
2026-10-29
DOI
https://doi.org/10.5281/zenodo.23750789
Primary Topic
Advanced Combinatorial Mathematics
Type
preprint
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preprint

An indecomposable equiprojective polytope with eleven vertices

John Seamons
Zenodo (CERN European Organization for Nuclear Research)
Advanced Combinatorial Mathematics
preprint

An indecomposable equiprojective polytope with eleven vertices

John Seamons
preprint en

Abstract

Buffière and Pournin asked whether a convex three-dimensional polytope can be both equiprojective and Minkowski indecomposable. We answer affirmatively with an eleven-vertex polytope whose coordinates belong to {−1, 0, 1}. Every orthogonal projection in a direction parallel to no facet is a heptagon. Its six triangular facets occur in translated pairs, and its six remaining facets are parallelograms; these features give a complete compensation pairing. Requiring edge vectors to close around these faces forces every Minkowski summand to be a translated scaled copy of the whole polytope. We describe the direct search route, give the exact geometry and elementary proofs, and supply a standalone Python verifier using rational arithmetic.

Zenodo (CERN European Organization for Nuclear Research)
Advanced Combinatorial Mathematics
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