Fröberg's conjecture on Hilbert series of generic ideals

Let k[x1,,xn]k[x_1,\dots,x_n] be a polynomial ring, and let I=(f1,,fr)I=(f_1,\dots,f_r) be a generic ideal whose generators satisfy degfi=di\deg f_i=d_i. For a power series F(T)F(T), write [F(T)][F(T)] for its truncation at the first nonpositive coefficient. Fröberg's conjecture. The Hilbert series of R/IR/I is

HR/I(T)=[i=1r(1Tdi)(1T)n].\operatorname{H}_{R/I}(T)=\left[\frac{\prod_{i=1}^r(1-T^{d_i})}{(1-T)^n}\right].

The conjecture predicts the Hilbert series of a generic ideal from the degrees of its generators and is equivalent to the expected maximal-rank behavior of a generic sequence of forms. The surrounding discussion relates it to semi-regular sequences, for which the predicted Hilbert series is known; the conjectural assertion for generic ideals remains unresolved in the stated generality.

Sources & referencesView supporting material

Primary source

Eric Dannetun, “Betti numbers of ideals generated by n+1 powers of general linear forms”, arXiv:2602.19978 (2026).

Additional references

19 papers in this index state this conjecture (2000–2026). The statement above is taken from the most recent of them; the others are arXiv:2504.13591, arXiv:2410.23211, arXiv:2311.05805, arXiv:2309.03855, arXiv:2102.11516, arXiv:1801.01692, arXiv:1711.05014, arXiv:1711.01232, arXiv:1711.05309, arXiv:1604.06820, arXiv:1512.04324, arXiv:1502.06762, and 6 more.

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