The regularity formula for squarefree powers of edge ideals of forests

Let GG be a forest. For a positive integer kk, let I(G)[k]I(G)^{[k]} denote the kkth squarefree power of the edge ideal of GG, let reg\operatorname{reg} denote Castelnuovo–Mumford regularity, let aim(G,k)\operatorname{aim}(G,k) denote the maximum cardinality of an induced kk-matching of GG, and let mat(G)\operatorname{mat}(G) denote the matching number of GG.

Forest regularity conjecture. For every 1kmat(G)1\leq k\leq \operatorname{mat}(G),

reg(I(G)[k])=aim(G,k)+k.\operatorname{reg}(I(G)^{[k]})= \operatorname{aim}(G,k)+k.

The conjecture proposes that the upper bound established for squarefree powers of edge ideals of forests is always sharp. It is motivated by the preceding results and Macaulay2 computations, but the source provides no resolution.

Sources & referencesView supporting material

Primary source

Nursel Erey and Takayuki Hibi, “Squarefree powers of edge ideals of forests”, arXiv:2105.09744 (2021).

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