REVIEW 2 major objections 4 minor 43 references
A proof of the Brian\c{c}on-Iarrobino Conjecture in three dimensions
T0 review · 2 major / 4 minor · reviewed 2026-08-15 · deepseek-v4-flash
Pith's one-line read The paper proves that for every tetrahedral number $l = \binom{k+2}{3}$, the Hilbert scheme $\mathrm{Hilb}^{l}(\mathbb{A}^{3})$ is most singular at the point cut out by the $k$-th power of the maximal ideal, resolving the 1978…
desk verdict The main idea is likely right, but a load-bearing lemma is unproved; the paper needs a real referee and a repaired proof before it can be accepted. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The argument works with the decomposition $I = \bigoplus_i x^{i} I_i$, where each $I_i$ is a monomial ideal in $\mathbb{C}[y,z]$; this is the filtration introduced in [37]. For two such ideals $J, J'$, the paper proves $\hom(J, S/J') = l + l' - \operatorname{Card}(B_n^{J,J'} \setminus A_n^{J,J'})$, where the subtracted term counts 'ghost vectors', connected components that lie in the upper half-plane but are unbounded and hence do not contribute to the tangent space. A computable lower bound for that term is $t(J, J')$, the number of monomials of $S/J'$ sitting at or above the height of $J'$. The new input is Corollary 2.2, which asserts $t(I_i, I_j) \geq \binom{j-i+1}{2}$ for the layers of any Borel-fixed ideal; summing these triangular lower bounds produces the term $2\binom{m_1+2}{4}$ that makes the earlier upper bound sharp.
What would settle it
Take the layers $I_i$ of every Borel-fixed ideal of small colength, compute $t(I_i, I_j)$ directly from the monomial sets, and check whether $t(I_i, I_j) \geq \binom{j-i+1}{2}$ holds in all cases; one pair with a smaller value, or one Borel-fixed ideal whose tangent-space dimension exceeds $\psi(m_1)$, would refute the central claim.
Extended reading notes
Core claim
The central result is Theorem A: for any 0-dimensional Borel-fixed ideal $I = (x^{m_1}, y^{m_2}, z^{m_3}, \text{mixed generators})$ of colength $l = \binom{k+2}{3}+\Delta$ with $0 \leq \Delta \leq \binom{k+2}{2}-1$, the tangent-space dimension satisfies $T(I) \leq (2m_1+1)l - 2\binom{m_1+2}{4}$. Theorem B states that the right-hand side, viewed as a function $\psi(m_1)$, is strictly increasing. Since Lemma 2.3 forces $m_1 \leq k$ in the tetrahedral range, one gets $T(I) \leq \psi(k)$. A direct computation gives $\psi(k) = \binom{k+2}{2}\binom{k+1}{2} = T(m_k)$, where $m_k = (x,y,z)^{k}$. Hence the tangent space at $[m_k]$ is at least as large as at any other point, and the maximum singularity of $\mathrm{Hilb}^{l}(\mathbb{A}^{3})$ occurs at $[m_k]$.
Load-bearing premise
The load-bearing premise is the unproved Corollary 2.2: for the two-variable ideals $I_i$ in the decomposition of a Borel-fixed ideal, the count $t(I_i, I_j)$ is always at least the triangular number $\binom{j-i+1}{2}$; if this inequality fails for some ideal, the paper's upper bound on $T(I)$ does not follow.
Editorial extensions
If this is right
- For each tetrahedral $l = \binom{k+2}{3}$, the point $[m_k]$ has tangent-space dimension exactly $\binom{k+2}{2}\binom{k+1}{2}$, and no point of $\mathrm{Hilb}^{l}(\mathbb{A}^{3})$ has a larger tangent space.
- Any maximally singular point of $\mathrm{Hilb}^{l}(\mathbb{A}^{3})$ at a tetrahedral $l$ must have smallest pure exponent $m_1 = k$, confirming the necessary condition proposed in [40].
- The upper bound $T(I) \leq (2m_1+1)l - 2\binom{m_1+2}{4}$ is valid for every Borel-fixed ideal whose colength lies in the interval $[\binom{k+2}{3}, \binom{k+3}{3}-1]$, giving a uniform estimate in that range.
- Because the upper bound is increasing in $m_1$ and equals the lower bound at $m_k$, the maximal singularity problem for tetrahedral $l$ is settled exactly, not up to a multiplicative constant.
Reading between the lines
- A reader who wants to verify the paper will find that Corollary 2.2 is the only step stated without proof; a direct combinatorial proof of $t(I_i, I_j) \geq \binom{j-i+1}{2}$ would make the argument self-contained, and a counterexample would destroy the theorem.
- The same ghost-vector correction is a natural template for higher dimensions: for $\mathrm{Hilb}^{l}(\mathbb{A}^{N})$ with $l = \binom{k+N-1}{N}$, the expected extremal ideal is the power $(x_1,\dots,x_N)^{k}$, and the correction terms should be higher binomial coefficients, a direction the paper does not pursue.
- The monotonicity of $\psi$ suggests that just above a tetrahedral number the maximizer should still have smallest pure exponent $k$; the announced sequel addresses certain non-tetrahedral $l$, but the mechanism here is already visible in the inequality $T(I) \leq \psi(m_1)$.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a proof of the 1978 Briançon-Iarrobino Conjecture for the Hilbert scheme Hilb^l(A^3) when l is a tetrahedral number. The strategy is to refine the Ramkumar-Sammartano upper bound for the tangent space by introducing a correction term, obtaining T(I) ≤ (2m1+1)l − 2 binom(m1+2,4) for every Borel-fixed ideal of colength l. The authors then prove that the function ψ(m1) defined by this bound is strictly increasing, and they combine this with the known value T(m_k) = ψ(k) to conclude that the maximum singularity occurs at [m_k]. The paper also derives a conjectural necessary condition for maximal singularity. The main technical ingredients are a decomposition I = ⊕ x^i I_i, a bound hom(J,S/J') ≤ l + l' − t(J,J'), and a purported lower bound t(I_i,I_j) ≥ binom(j-i+1,2).
Significance. If the proof is completed, the result resolves a major conjecture in the study of Hilbert schemes of points, open since 1978, and it supplies a clean explanation of why the maximum singularity occurs at the tetrahedral ideal m_k. The overall strategy is attractive, and the arithmetic identity ψ(k) = T(m_k) checks out. The paper is clearly organized and the examples in Section 1 are helpful. However, the central new combinatorial inequality, Corollary 2.2, is stated without proof and is used essentially in the proof of Theorem A; this is a load-bearing gap in the current version.
major comments (2)
- [Section 2, Corollary 2.2] The inequality binom(j-i+1,2) ≤ t(I_i,I_j) is asserted without proof, and it is exactly the term that makes the final bound sharp. In the proof of Theorem A, after applying Corollary 1.15, the displayed chain passes through ≤ (2m1+1)l − Σ_{0≤i<j≤m1-1} binom(j-i+1,2) − binom(m1+2,4). This step is legitimate only if Corollary 2.2 holds. The text offers no derivation: Lemma 2.1 concerns shifts α with α_x<0 and minimal generators γ, whereas t(I_i,I_j) is defined from the yz-slices and the height of I_j, and the bridge between these statements is not exhibited. Example 1.17 verifies equality for the extremal ideal m_k only, and Example 1.16 exhibits strict inequality in another case; neither establishes the general lower bound. Since this is the load-bearing novelty of the paper, the proof of Theorem A is incomplete as written. Please supply a complete proof of Corollary 2.2.
- [Section 1, Lemma 1.5, Claim 2] The well-definedness of g is not established. The proof defines g: B^{J,J'}_n → N^2 \ \tilde J by (U,α) ↦ (γ_y, −α_z−1) and must show (γ_y, −α_z−1) ∉ \tilde J. The text says that because U lies in the upper half-plane, γ_z+α_z+1>0, hence γ_z > −α_z−1, 'and so f(U,α)/∈ J'. This conclusion does not follow: \tilde J is upward closed, so the inequality γ_z > −α_z−1 gives no information about whether the smaller-height point (γ_y, −α_z−1) lies in \tilde J. One needs an argument using the maximality of γ_y (and minimality of γ_z among ties) to rule out (γ_y, −α_z−1) ∈ \tilde J; no such argument is supplied. Since the bijection B^{J,J'}_n ≅ N^2 \ \tilde J underlies the exact count in Corollary 1.9 and hence the bound in Lemma 1.5, this gap also affects the proof of Theorem A.
minor comments (4)
- [Section 1, proof of Lemma 1.5] In the proof of Claim 2, the displayed statement 'and so f(U,α)/∈ J' should read 'and so g(U,α) ∉ \tilde J'; the function being defined is g, not f.
- [Section 2, proof of Theorem A] The proof of the Claim is very terse: from (2.1) and (2.2) it asserts that the relevant components form a single bounded connected component and a single unbounded component, but the details of this implication are not spelled out. Please expand this step.
- [Section 2, proof of Theorem B] The derivative computation is correct, but the positivity step would be clearer if written as follows: for fixed k and ∆ ≥ 0, the displayed expression is decreasing in m1, so its minimum occurs at m1 = k, where it equals 3k^2 + 5k + 1 + 12∆ > 0.
- [Section 1, Definition 1.1] The phrase 'xy−z-octant' is nonstandard; consider replacing it with 'the first octant of the (x,y,z) lattice' or similar wording.
Circularity Check
No circularity: the upper bound is proved from combinatorial lemmas, and the sharpness check T(m_k)=ψ(k) uses external classical computations.
full rationale
Walked the claimed derivation chain. Theorem A is an upper bound proved by decomposing I = ⊕ x^i I_i, expanding T(I) over pairs Hom(I_i, S/I_j), subtracting zero-vector counts via the Claim and identity (2.3), and applying Corollary 1.15 together with the asserted lower bound t(I_i,I_j) ≥ binom(j-i+1,2). The latter is labelled Corollary 2.2 but no proof is displayed; this is a missing-support correctness gap, not circularity, because t is defined independently from the set {β ∈ N^2 \ tilde I_0 : β_z ≥ h}, and the asserted inequality is not identical to the theorem's conclusion. The sharp comparison T(m_k)=ψ(k) is obtained from [5, Proposition III.4] or [40, Corollary 1.9]; [5] is an external classical computation, and the formula is not fitted from the data being predicted. The self-citation [40, Lemma 1.7] enters only in the short argument for Corollary 2, not in the proof of the Briançon-Iarrobino Conjecture; even if that argument is incomplete, the main bound does not reduce to a self-citation. No parameter is fitted and then renamed a prediction: ψ is an explicit function of l and m_1, and Theorem B's monotonicity is proven from Lemma 2.3. Thus no circular step is exhibited, and the correct circularity finding is score 0.
Assumptions & free parameters
assumptions (4)
- domain assumption For every l there exists a Borel-fixed ideal of colength l that attains the maximal tangent space dimension (Remark 0.4).
- domain assumption The tangent space at [I] has dimension hom(I,R/I), and T(m_k) = binom(k+2,2) binom(k+1,2) from [5, Proposition III.4] or [40, Corollary 1.9].
- standard math Borel-fixed ideals satisfy the strong stability rule used in Lemma 2.1: if a minimal generator gamma and alpha with alpha_x < 0 satisfy gamma + alpha in tilde I, then gamma - e_x in tilde I.
- standard math All work is over a characteristic 0 field, and C can be replaced by any characteristic 0 field (Remark 0.1).
Cite this review
Pith. "Pith review of A proof of the Brian\c{c}on-Iarrobino Conjecture in three dimensions." pith.science (2026). https://pith.science/paper/Q2HJYXYG
@misc{pith2026250821717,
author = {Pith},
title = {Pith review of: A proof of the Brian\ccon-Iarrobino Conjecture in three dimensions},
year = {2026},
howpublished = {\url{https://pith.science/paper/Q2HJYXYG}},
note = {Machine review of arXiv:2508.21717}
}
abstract
We resolve the 1978 Brian\c{c}on-Iarrobino Conjecture regarding the maximum singularity of $\mathcal{H}=\mathrm{Hilb}^{l}(\mathbb{A}^3)$, where $l$ is a tetrahedral number, by refining the work of Ramkumar-Sammartano in \cite{Ramkumar-Sammartano}. This also immediately implies the conjectural necessary condition for a point of $\mathcal{H}$ to have the maximal singularity, suggested by the second-named author in \cite{Rezaee-23-Conjectures}. In a sequel to this article, \cite{Mackenzie-Rezaee2}, we prove a generalized version of this conjecture for certain non-tetrahedral $l$, via proving the conjectural necessary condition.
Reference graph
Works this paper leans on
-
[40]
F . Rezaee,Conjectural criteria for the most singular points of the Hilbert schemes of points , Experimental Mathematics, Online first. https://doi.org/10.1080/10586458.2024.2400181. arXiv:2312.04520 (2024), 1–16
arXiv 2024
-
[5]
J. Briançon and A. Iarrobino, Dimension of the punctual Hilbert scheme, J. Algebra 55 (1978), 536–544
work page 1978
-
[37]
R. Ramkumar and A. Sammartano, On the tangent space to the Hilbert scheme of points in P3, Transactions of the American Mathematical Society 375 (2022), 6179–6203
work page 2022
- [1]
- [2]
-
[3]
K. Behrend, J. Bryan, and B. Szendr˝oi, Motivic degree zero Donaldson–Thomas invariants, Invent. Math. 192 (2013), no. 1, 111–160
work page 2013
-
[4]
K. Behrend and B. Fantechi,Symmetric obstruction theories and Hilbert schemes of points on threefolds, Algebra Number Theory 2 (2008), 313–345
work page 2008
-
[6]
D. Cartwright, D. Erman, M. Velasco, and B. Viray,Hilbert schemes of 8 points, Algebra Number Theory 3 (2009), no. 7, 763–795
work page 2009
Show all 43 references
-
[7]
Douvropoulos, J
T . Douvropoulos, J. Jelisiejew, B. I. U. Nødland, and Z. Teitler,The Hilbert scheme of 11 points inA3 is irreducible, Combinatorial algebraic geometry, Fields Inst. Commun., vol. 80, Fields Inst. Res. Math. Sci., Toronto, ON, 2017, pp. 321–352
2017
-
[8]
Farkas, R
G. Farkas, R. Pandharipande, and A. Sammartano, Irrational components of the Hilbert scheme of points , arXiv:2405.11997 (2024)
2024 arXiv
-
[9]
Fogarty, Algebraic families on an algebraic surface, Amer
J. Fogarty, Algebraic families on an algebraic surface, Amer. J. Math. 60 (1968), 511–521
1968
-
[10]
Giovenzana, L
F . Giovenzana, L. Giovenzana, M. Graffeo, and P . Lella,A counterexample to the parity conjecture, Algebraic geometry 12 (2025), no. 2, 173–188
2025
-
[11]
Gorsky and A
E. Gorsky and A. Negu¸ t,Refined knot invariants and Hilbert schemes , Journal de Mathématiques Pures et Appliquées 104 (2015), no. 3, 403–435
2015
-
[12]
D. R. Grayson and M. E. Stillman, Macaulay2, a software system for research in algebraic geometry, Available at http://www.math.uiuc.edu/Macaulay2/
-
[13]
Grojnowski, Instantons and affine algebras I: The Hilbert scheme and vertex operators, Math
I. Grojnowski, Instantons and affine algebras I: The Hilbert scheme and vertex operators, Math. Res. Letters 3 (1996), no. 275
1996
-
[14]
Gross and F
M. Gross and F . Rezaee,Bridgeland wall-crossing for Hilbn (P2) from scattering diagram, in preparation (2025)
2025
-
[15]
Gross and F
M. Gross and F . Rezaee,Decomposition of stability scattering diagram for P2 and its applications, to appear (2025)
2025
-
[16]
Grothendieck, Techniques de construction et théorèmes d’existence en géométrie algébrique iv, Séminaire Bourbaki 6 (1995), no
A. Grothendieck, Techniques de construction et théorèmes d’existence en géométrie algébrique iv, Séminaire Bourbaki 6 (1995), no. 221, 249–276
1995
-
[17]
Haiman, t, q-Catalan numbers and the Hilbert scheme, Discrete Mathematics 193 (1998), no
M. Haiman, t, q-Catalan numbers and the Hilbert scheme, Discrete Mathematics 193 (1998), no. 1, 201–224
1998
-
[18]
Haiman, Hilbert schemes, polygraphs and the MacDonald positivity conjecture, Journal of the American Mathematical Society 14 (2001), no
M. Haiman, Hilbert schemes, polygraphs and the MacDonald positivity conjecture, Journal of the American Mathematical Society 14 (2001), no. 4, 941–1006
2001
-
[19]
Hartshorne, Connectedness of the hilbert scheme, Publ
R. Hartshorne, Connectedness of the hilbert scheme, Publ. Math. Inst. Hautes Études Sci. 29 (1966), 5–48
1966
-
[20]
A. A. Henni and M. Jardim, Commuting matrices and the Hilbert scheme of points on affine spaces, Adv. Geom. 18 (2018), no. 4, 467–482
2018
-
[21]
Hu, On singular Hilbert schemes of points: local structures and tautological sheaves, arXiv:2101.05236 (2021)
X. Hu, On singular Hilbert schemes of points: local structures and tautological sheaves, arXiv:2101.05236 (2021)
2021 arXiv
-
[22]
Huizenga, Effective divisors on the hilbert scheme of points in the plane and interpolation for stable bundles, J
J. Huizenga, Effective divisors on the hilbert scheme of points in the plane and interpolation for stable bundles, J. Algebraic Geom. 25 (2016), 19–75
2016
-
[23]
J. W . Huizenga,Restrictions of Steiner bundles and divisors on the Hilbert scheme of points in the plane (PhD thesis), Harvard University (2012)
2012
-
[24]
Iarrobino, Reducibility of the families of 0-dimensional schemes on a variety, Invent
A. Iarrobino, Reducibility of the families of 0-dimensional schemes on a variety, Invent. Math. 15 (1972), 72–77
1972
-
[25]
Jelisiejew, Pathologies on the Hilbert scheme of points, Invent
J. Jelisiejew, Pathologies on the Hilbert scheme of points, Invent. Math. 220 (2020), no. 2, 581–610. A PROOF OF THE 1978 BRIANÇON-IARROBINO CONJECTURE IN THREE DIMENSIONS 13
2020
-
[26]
Jelisiejew, M
J. Jelisiejew, M. Kool, and R. F . Schmiermann,Behrend’s function is not constant on Hilbn (C3), To appear in Geometry and Topology, arXiv:2311.05408 (2023)
2023
-
[27]
Jelisiejew, R
J. Jelisiejew, R. Ramkumar, and A. Sammartano,The Hilbert scheme of points on a threefold, I, arXiv:2409.17009 (2024)
2024 arXiv
-
[28]
Katz, The desingularization of Hilb4(P3) and its Betti numbers, Zero-dimensional schemes (Ravello, 1992) (1994), 231–242
S. Katz, The desingularization of Hilb4(P3) and its Betti numbers, Zero-dimensional schemes (Ravello, 1992) (1994), 231–242
1994
-
[29]
Li and X
C. Li and X. Zhao, The MMP for deformations of Hilbert schemes of points on the projective plane, Algebraic Geometry 5 (2018), no. 3, 328–358
2018
-
[30]
Li and X
C. Li and X. Zhao, Birational models of moduli spaces of coherent sheaves on the projective plane, Geometry and Topology 23 (2019), 347–426
2019
-
[31]
Mackenzie and F
O. Mackenzie and F . Rezaee,Maximal singularities of the Hilbert scheme of a non-tetrahedral number of points in three dimensions, in preparation (2025)
2025
-
[32]
Maulik, N
D. Maulik, N. Nekrasov, A. Okounkov, and R. Pandharipande,Gromov–Witten theory and Donaldson–Thomas theory, I, Compos. Math. 142 (2006), no. 5, 1263–1285
2006
-
[33]
Miller and B
E. Miller and B. Sturmfels, Combinatorial commutative algebra, vol. 227, Graduate Texts in Mathematics, Springer-Verlag, New York, 2005
2005
-
[34]
Nesterov, Hilbert schemes of points and Fulton-MacPherson compactifications, arXiv:2501.08269 (2025)
D. Nesterov, Hilbert schemes of points and Fulton-MacPherson compactifications, arXiv:2501.08269 (2025)
2025 arXiv
-
[35]
Pandharipande, A tour of the geometry of points in affine space, DMV Jahrestagung lecture (2022)
R. Pandharipande, A tour of the geometry of points in affine space, DMV Jahrestagung lecture (2022)
2022
-
[36]
Pandharipande and R
R. Pandharipande and R. P . Thomas,Curve counting via stable pairs in the derived category, Invent. Math. 178 (2009), no. 2, 407–447
2009
-
[38]
Ramkumar and A
R. Ramkumar and A. Sammartano, Rational singularities of nested Hilbert schemes , International Mathematics Research Notices (2024), no. 2, 1061–1122
2024
-
[39]
Ramkumar and A
R. Ramkumar and A. Sammartano, On the parity conjecture for Hilbert schemes of points on threefolds, Annali della Scuola Normale Superiore di Pisa, Classe di Scienze XXVI (2025), no. 3
2025
-
[41]
A. T . Ricolfi, A sign that used to annoy me, and still does, J. Geom. Phys. 125 (2024)
2024
-
[42]
Sturmfels, Four Counterexamples in Combinatorial Algebraic Geometry , Journal of Algebra 230 (2000), 282–294
B. Sturmfels, Four Counterexamples in Combinatorial Algebraic Geometry , Journal of Algebra 230 (2000), 282–294
2000
-
[43]
Vakil, Murphy’s law in algebraic geometry: badly-behaved deformation spaces , Invent
R. Vakil, Murphy’s law in algebraic geometry: badly-behaved deformation spaces , Invent. Math. 164 (2006), no. 3, 569–590. CENTRE FOR MATHEMATICAL SCIENCES , UNIVERSITY OF CAMBRIDGE , WILBERFORCE ROAD, CB3 0WA, CAMBRIDGE , UNITED KINGDOM Email address: om379@cam.ac.uk Email ad...
2006
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