Minimality conjecture for Hilbert depth differences of squarefree monomial ideals

Let KK be a field, let S=K[x1,,xn]S=K[x_1,\ldots,x_n], and let ISI\subset S be a squarefree monomial ideal. Write

hdepth(S/I)=q.\operatorname{hdepth}(S/I)=q.

For each integer d0d\geq 0, let n(d)n(d) and m(d)m(d) be the smallest integers for which

hdepth(S/In(d),m(d))hdepth(In(d),m(d))=d,\operatorname{hdepth}(S/I_{n(d),m(d)})-\operatorname{hdepth}(I_{n(d),m(d)})=d,

and set

q(d)=hdepth(S/In(d),m(d)).q(d)=\operatorname{hdepth}(S/I_{n(d),m(d)}).

Minimality conjecture. If q<q(d)q<q(d) or n<n(d)n<n(d), then

hdepth(S/I)hdepth(I)d+1.\operatorname{hdepth}(S/I)\geq \operatorname{hdepth}(I)-d+1.

The conjecture asserts that the ideals In,mI_{n,m} provide the smallest examples, with respect to both the number of variables and hdepth(S/I)\operatorname{hdepth}(S/I), for a prescribed difference d=hdepth(S/I)hdepth(I)d=\operatorname{hdepth}(S/I)-\operatorname{hdepth}(I). The statement remains open in the supplied source; its status is based on the authors' formulation as a proposed conjecture rather than on a resolution result.

Sources & referencesView supporting material

Primary source

Andreea I. Bordianu and Mircea Cimpoeas, “Comparing Hilbert depth of I with Hilbert depth of S/I. III”, arXiv:2407.04759 (2026).

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