A Six-Vertex Counterexample to Vertex-Averaged Ordered Reachability

We give two loopless directed graph layers on six vertices, each with constant outdegree two, having no rainbow directed cycle and hence no increasing rainbow cycle. For the fixed label order 1<2, the sizes of the sets reachable by possibly trivial increasing paths are 5,5,5,5,5,4. Their average is 29/6<5=1+delta_1+delta_2. Thus the uniform-start-vertex interpretation of the ordered-reachability conjecture attributed to DeVos in Sullivan's 2006 survey is false. Uniform blow-ups give examples on 6m vertices with average 1+23m/6, below the proposed bound 1+4m for every m>=1. The proof is an explicit neighborhood calculation and does not depend on the numerical search that located the example. Unrefereed preprint. The original source does not specify its averaging variable. This result addresses a fixed label order and a uniform average over starting vertices, not averaging over label orders. It does not disprove the Caccetta-Haggkvist conjecture or its unordered rainbow-path analogue. The source package includes an exact standard-library Python verifier and archived results. No independent peer review, formal verification, or absolute priority certificate is claimed. AI-assisted tools supported research, computation, proof development and writing; the author is responsible for the final text. Corpus identifier: AIM-COMBINATORICS-0177.

Authors

Publication Details

Journal
Zenodo (CERN European Organization for Nuclear Research)
Published
2026-09-28
DOI
https://doi.org/10.5281/zenodo.23016086
Primary Topic
Advanced Graph Theory Research
Type
preprint
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preprint

A Six-Vertex Counterexample to Vertex-Averaged Ordered Reachability

Alper Ferudun
Zenodo (CERN European Organization for Nuclear Research)
Advanced Graph Theory Research
preprint

A Six-Vertex Counterexample to Vertex-Averaged Ordered Reachability

Alper Ferudun
preprint en

Abstract

We give two loopless directed graph layers on six vertices, each with constant outdegree two, having no rainbow directed cycle and hence no increasing rainbow cycle. For the fixed label order 1<2, the sizes of the sets reachable by possibly trivial increasing paths are 5,5,5,5,5,4. Their average is 29/6<5=1+delta_1+delta_2. Thus the uniform-start-vertex interpretation of the ordered-reachability conjecture attributed to DeVos in Sullivan's 2006 survey is false. Uniform blow-ups give examples on 6m vertices with average 1+23m/6, below the proposed bound 1+4m for every m>=1. The proof is an explicit neighborhood calculation and does not depend on the numerical search that located the example. Unrefereed preprint. The original source does not specify its averaging variable. This result addresses a fixed label order and a uniform average over starting vertices, not averaging over label orders. It does not disprove the Caccetta-Haggkvist conjecture or its unordered rainbow-path analogue. The source package includes an exact standard-library Python verifier and archived results. No independent peer review, formal verification, or absolute priority certificate is claimed. AI-assisted tools supported research, computation, proof development and writing; the author is responsible for the final text. Corpus identifier: AIM-COMBINATORICS-0177.

Zenodo (CERN European Organization for Nuclear Research)
Advanced Graph Theory Research
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A Six-Vertex Counterexample to Vertex-Averaged Ordered Reachability — Alper Ferudun · Zenodo (CERN European Organization for Nuclear Research) (2026) | TGRS Research Map | TGRS