Belkhechine–Bouaziz–Boudabbous–Pouzet conjecture for path-reversed tournaments

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Let QnQ_n be the tournament on [n]={1,…,n}[n]=\{1,\ldots,n\} obtained from the natural transitive tournament by reversing precisely the consecutive pairs 12,23,…,(n−1)n12,23,\ldots,(n-1)n. Equivalently, for i<ji<j, orient i→ji\to j when j≥i+2j\geq i+2, and orient i+1→ii+1\to i when j=i+1j=i+1. Here inv⁡(D)\operatorname{inv}(D) denotes the minimum size of a family of vertex-set inversions whose application produces an acyclic, equivalently transitive, tournament. Belkhechine–Bouaziz–Boudabbous–Pouzet conjecture. The inversion number of QnQ_n is

inv⁡(Qn)=⌊n−12⌋.\operatorname{inv}(Q_n)=\left\lfloor\frac{n-1}{2}\right\rfloor.

This conjecture concerns the exact number of induced subtournament reversals needed to make the structured tournament QnQ_n transitive. The supplied source does not state its resolution; the status is therefore left open.

References

Primary source

Yaping Mao, “The inversion number of a path-reversed tournament: Resolving a conjecture of Belkhechine, Bouaziz, Boudabbous, and Pouzet”, arXiv:2607.13829 (2026).

Additional references

2 papers in this index state this conjecture (2022–2026). The statement above is taken from the most recent of them; the others are arXiv:2212.11969.

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