Rinaldo–Romeo thinness conjecture for rook polynomials of polyominoes

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Let P\mathcal{P} be a polyomino. Write rP(t)r_{\mathcal{P}}(t) for its rook polynomial, r(P)r(\mathcal{P}) for its rook number, hK[P](t)h_{K[\mathcal{P}]}(t) for the hh-polynomial of its coordinate ring, and reg⁡K[P]\operatorname{reg} K[\mathcal{P}] for its regularity. A polyomino is thin when it has the thinness property defined in the source.

Rinaldo–Romeo conjecture. The polyomino P\mathcal{P} is thin if and only if

rP(t)=hK[P](t).r_{\mathcal{P}}(t)=h_{K[\mathcal{P}]}(t).

Moreover, the source asks whether

reg⁡K[P]=r(P).\operatorname{reg} K[\mathcal{P}]=r(\mathcal{P}).

For simple thin polyominoes, the equality of the hh-polynomial with the rook polynomial and the equality of regularity with the rook number are known. The conjecture asks whether the polynomial characterization extends to all polyominoes and whether the regularity equality holds in general.

References

Primary source

Francesco Navarra and Ayesha Asloob Qureshi, “Recent Advances in the Theory of Polyomino Ideals”, arXiv:2511.22778 (2025).

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