REVIEW 3 major objections 6 minor 1 cited by
Richardson tableaux and Schubert positivity
T0 review · 3 major / 6 minor · reviewed 2026-08-04 · deepseek-v4-flash
Pith's one-line read This paper proves that for every Richardson tableau T, the Schubert-cycle expansion of the Springer fiber component X^{w_T}_{v_T} is computed by a combinatorial rule: count saturated chains in k-Bruhat order after translating the Bruhat int
desk verdict The well-aligned-pair framework is the real new idea and it works, but the proof as written has a load-bearing hole: Corollary 4.12 is stated without proof and is the only bridge to Richardson tableaux. 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 central object is the class of well-aligned pairs (v,w) in S_n × S_n: pairs such that v^{-1}(1) ≤ w^{-1}(1), every index between is an ascent of v, and the property is preserved by deleting the letter 1 from both permutations. The load-bearing identity is the translation-equivalence [v,w] ≅ [v^↑, v^↑v^{-1}w], where v^↑ is the unique dominant permutation in the same plane-binary-tree fiber as v; this reduces Schubert structure coefficients to multiplication by a dominant monomial, computed by Sottile's Pieri rule as a sum over saturated chains in k-Bruhat order. A second, independent mechanism expresses the same coefficients as a composition of divided differences ∂_i and Bergeron–Sottile
What would settle it
Take the Richardson tableau T of Example 4.2, compute S_{v_T}S_u by direct divided-difference expansion for several u, and compare the coefficient of each Schubert polynomial with the number of saturated k-Bruhat chains prescribed by Corollary 3.3; any mismatch would refute Theorem 0.1. A more targeted check: verify Proposition 2.12 for a well-aligned pair such as (15726348,75182364) by applying the swaps in C(v) in every order and confirming that all paths terminate at v^↑ = 56734128; if some order fails to reach it, the translation-equivalence argument collapses.
Extended reading notes
Core claim
The paper establishes Theorem 0.1: if T is a Richardson tableau, then c^{w_T}_{u,v_T}—the coefficient of the Schubert class [X_u] in the expansion of [X^{w_T}_{v_T}]—is computed combinatorially. The proof introduces well-aligned pairs (v,w): pairs where the positions of 1 are ordered, all intermediate positions are ascents in v, and the property persists after deleting the letter 1. For these pairs, Proposition 2.12 shows the Bruhat interval [v,w] is left-translation equivalent to [v^↑, v^↑v^{-1}w] with v^↑ dominant, so c^w_{u,v}=c^{v^↑v^{-1}w}_{u,v^↑} by Fact 1.7. Since v^↑ is dominant, S_{v^↑} is a dominant monomial, and Corollary 3.3 expresses the product S_{v^↑}S_u as a positive sum of S
Load-bearing premise
The proof rests on two unproved steps: that repeatedly swapping adjacent 'critical' letters always transforms v into its dominant representative v^↑ (used in Proposition 2.12), and that the omitted proof of Corollary 4.12 correctly describes the descents of v_T and w_T—if either fails, the main rule has no foundation.
Editorial extensions
If this is right
- The Schubert-cycle class [X^{w_T}_{v_T}] of any Richardson-tableau Springer component is now explicitly computable as a nonnegative sum of Schubert cycles, by counting saturated chains in k-Bruhat order.
- The same rule applies to every well-aligned pair, a class strictly larger than Richardson tableau pairs (for example, pairs from quasisymmetric coinvariants), giving new cases of Schubert positivity.
- The Bergeron–Sottile/divided-difference factorization gives a second algorithm and a geometric construction of X^w_v via inclusions and push-pulls, so the two algorithms can be cross-checked.
- Richardson varieties X^w_v attached to very well-aligned pairs are smooth; for Richardson tableaux this recovers, and extends, the Karp–Precup smoothness theorem.
Reading between the lines
- The well-aligned condition is defined purely in permutation terms and does not mention tableaux; the paper's results suggest it is a natural combinatorial umbrella for Schubert-positivity-by-translation, and one could test whether other families of permutation pairs beyond Richardson tableaux satisfy it—for example, by enumerating WA_n via the conjectured functional equation.
- The equivalence of the two algorithms (translation plus Pieri versus divided differences plus R_i evaluations) hints at an explicit bijection between saturated chains in k-Bruhat order and the words produced by the R_i/∂_i factorization; finding it would give a new proof of a Pieri-type rule.
- The conjectured functional equation W'(x)=W(x)^2/(2-W(x)) for the number of well-aligned pairs suggests a recursive decomposition of pointed well-aligned pairs; if proven, it could lead to a direct enumeration of Richardson-tableau families and their Schubert coefficients.
- Since evacuation is an involution and v_T is read from evac(T), the rule is symmetric in a way that might allow immediate computation for T and evac(T); this could be exploited to give closed forms for the expansion in terms of the column-strip decomposition.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces a class of pairs of permutations (v,w), called well-aligned, and proves that for such pairs the Bruhat interval [v,w] is left-translation equivalent to an interval [v^↑, v^↑ v^{-1}w] whose bottom permutation v^↑ is dominant (Proposition 2.12). Since Schubert polynomials of dominant permutations are monomials, iteration of Sottile's Pieri rule yields an explicit, manifestly nonnegative combinatorial computation of the Schubert structure coefficients c^w_{u,v} (Theorem 3.4, Corollary 3.3); a second computation via Bergeron–Sottile operators is also given. The paper then connects this framework to Karp–Precup's Richardson tableaux: for a Richardson tableau T, the permutations v_T and w_T defined from reading words of evac(T) and T are shown to be very well-aligned (Lemma 4.14), yielding a combinatorial rule for the Schubert cycle expansion of the corresponding Richardson variety / Springer fiber component (Theorem 0.1). The last part gives geometric interpretations, a smoothness theorem for very well-aligned Richardson varieties, and two enumerative conjectures.
Significance. If correct, the paper answers Karp–Precup's Problem 10.4 and generalizes Güemes's hook-shape computation to all Richardson tableaux. The proposed rule is combinatorial and manifestly positive: it counts saturated chains in k-Bruhat order. The paper also isolates a new class of pairs with computable Schubert coefficients and proves a smoothness criterion. The main computational ingredients (Sottile's Pieri rule, Bergeron–Sottile maps) are standard and well matched to the problem. However, the bridge from Richardson tableaux to the well-aligned framework currently rests on an explicitly omitted proof (Corollary 4.12), so the main theorem is not yet fully established. The result is plausible and consistent with the examples, but the missing argument is load-bearing.
major comments (3)
- [§4, Corollary 4.12] The proof of Corollary 4.12 is explicitly omitted: 'We omit the proof as it amounts to unraveling Definition 4.4.' This corollary is load-bearing: Lemma 4.14 uses it to identify the positions of 1,...,k in v_T and w_T and to control their descent sets, and Lemma 4.14 is the only route from Richardson tableaux to the well-aligned framework of Theorem 3.4. Without a proof or a precise reference, Theorem 0.1 is conditional. The statement is plausible and matches the examples, so I view this as a missing-argument gap rather than a false claim. Please supply a complete proof, including the descent-set containments.
- [§2.2, Proposition 2.12] The proof asserts that because all linear extensions of a tree poset are connected by swaps of adjacent incomparable labels, repeated application of simple transpositions indexed by the current critical set transforms v into v^↑. This reachability claim is not proved; it is not immediate from the definition of C(w), and after each swap the critical set changes. Since Proposition 2.12(2) is the basis for the translation equivalence used in Theorem 3.4, please provide a self-contained argument or a precise citation that establishes exactly this statement.
- [§4, Lemma 4.14] The equality (δ^k(v_T), δ^k(w_T)) = (v_crop(T), w_crop(T)) is asserted with only a brief explanation. This equality is essential for the inductive step of very well-alignedness, and it relies on crop(evac(T)) = evac(crop(T)) and on the precise positions from Corollary 4.12. Please expand this argument; as written it is too terse to verify.
minor comments (6)
- [Definition 1.4] In the definition of translation-equivalent intervals, the second set should be {p^{-1}r | r ∈ [p,q]}, not {p^{-1}r | r ∈ [u,v]}.
- [Definition 4.13] The phrase 'if (v w_o, u w_o) is well-aligned' appears to contain a typo; it should read (v w_o, w w_o).
- [§5.2] The formula 'Ψ_{1,i} X_w^v = X_{ε_i(w)}^{ε_i(w)}' should presumably be X_{ε_i(v)}^{ε_i(w)}.
- [§5.3, Theorem 5.8 proof] In the first paragraph, smoothness is attributed to 'v'B' but Lemma 5.6 gives smoothness at w'B; the transfer to wB should use w'B. In the second paragraph, the anti-isomorphism from [ww_o, vw_o] to [v,w] maps vw_oB to vB, not wB, so the displayed 'if and only if' should refer to vB. Also, 'Theorem 5.6' and 'Theorem 5.4' should be 'Lemma 5.6' and 'Fact 5.4', respectively.
- [Corollary 4.12(2)] The notation Des(w_T) ⊆ {M_1, ..., M_k}^c is ambiguous; please clarify the complement (presumably in [n-1]).
- [Various] Minor typos: 'tableux criterion' in Lemma 2.4, 'evacuations slides' in Lemma 4.6, 'the the well-aligned pair' in Example 4.16, and the reference to 'Theorem 5.6' instead of 'Lemma 5.6' in Theorem 5.8.
Circularity Check
No circularity: the coefficients are externally defined via Schubert polynomial multiplication, and the main computation reduces to Sottile's Pieri rule via an internally proved translation equivalence.
full rationale
The Schubert structure coefficients c^w_{u,v} are defined externally by the identity S_u S_v = sum_w c^w_{u,v} S_w (Section 1.4, Section 5), not by any quantity that the paper later claims to predict. There is no fitted parameter or normalization that is renamed as a result. The main theorem (Theorem 3.4) is proved by showing that a well-aligned pair (v,w) has a Bruhat interval translation-equivalent to [v^up, v^up v^{-1}w] with v^up dominant; this reduction is established internally in Lemmas 2.4-2.12 using standard facts about Bruhat order and the tableau criterion, and the final coefficient computation uses Sottile's Pieri rule, an independent external theorem. The connection from Richardson tableaux to well-aligned pairs is Lemma 4.14, which relies on Corollary 4.12. Corollary 4.12 is explicitly stated as having an omitted proof ('We omit the proof as it amounts to unraveling Definition 4.4'). This is a missing proof and therefore a correctness risk, not a circular reduction: it does not assume the target coefficients or define them in terms of themselves. The paper does cite the authors' own prior work, notably [34, Proposition 8.1] for the Bergeron-Sottile recursion and [34, Theorem 4.4] for the geometric inclusion map, but these are used in an alternative computational route and in geometric interpretations, not in the combinatorial proof of Theorem 3.4; they are independent published results and are not the same as the target statement. No step in the derivation chain reduces by construction to its own input, so the paper has no significant circularity.
Assumptions & free parameters
assumptions (7)
- standard math Tableau criterion for Bruhat order (Theorem 1.3): u ≤_B v iff u_{i,k} ≤ v_{i,k} for all i,k; improved criterion suffices over k ∈ Des(u).
- domain assumption Fact 1.7: translation-equivalent Bruhat intervals have identical Schubert structure coefficients c^w_{u,v} = c^{w'}_{u,v'}.
- standard math Sottile's Pieri rule (Theorem 3.2): x_1...x_k S_u = Σ_{u →_k w} S_w; Corollary 3.3 iterates it for dominant monomials.
- domain assumption Karp-Precup characterization of Richardson tableaux by L-slides (Theorem 4.3(1)) and evacuation-invariance (Theorem 4.3(2)).
- domain assumption In a fiber Z_T of the plane-binary-tree bijection, there is a unique dominant permutation w^↑, and any linear extension can be brought to it by swapping critical values i and i+1.
- standard math Deodhar's smoothness criterion (Proposition 5.5) and Karp-Precup's criterion reducing smoothness of X^w_v to the two T-fixed points vB and wB (Fact 5.4).
- standard math For dominant v, v ≤_B w iff R(v) ⊆ R(w) (equation 2.1), and Rothe diagrams describe coordinate subspaces in Bruhat cells.
Cite this review
Pith. "Pith review of Richardson tableaux and Schubert positivity." pith.science (2026). https://pith.science/paper/342MROCL
@misc{pith2026251012391,
author = {Pith},
title = {Pith review of: Richardson tableaux and Schubert positivity},
year = {2026},
howpublished = {\url{https://pith.science/paper/342MROCL}},
note = {Machine review of arXiv:2510.12391}
}
read the original abstract
We compute the Schubert cycle expansion of those irreducible components of Springer fibers equal to Richardson varieties. This generalizes work of G\"uemes in the case of a hook shape and answers a question of Karp-Precup.
Forward citations
Cited by 1 Pith paper
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The Springer Geometry of Specht Polynomials and Schubert cycle positivity for two row Springer fiber components
Two-row Springer fiber components have positive Schubert cycle expansions counted by reduced words compatible with noncrossing matchings.
Reference graph
Works this paper leans on
-
[1]
Aguiar and F
M. Aguiar and F. Sottile. Structure of the Loday-Ronco Hopf algebra of trees.J. Algebra, 295(2):473–511, 2006. 10
2006
-
[2]
Alman, C
J. Alman, C. Lian, and B. Tran. Circular planar electrical networks: posets and positivity.J. Combin. Theory Ser. A, 132:58–101, 2015. 24
2015
-
[3]
Anderson and W
D. Anderson and W. Fulton.Equivariant cohomology in algebraic geometry, volume 210 ofCambridge Studies in Ad- vanced Mathematics. Cambridge University Press, Cambridge, 2024. 20
2024
-
[4]
N. Bergeron, L. Gagnon, P . Nadeau, H. Spink, and V . Tewari. Equivariant quasisymmetry and noncrossing parti- tions, 2025, 2504.15234. 2
arXiv 2025
-
[5]
N. Bergeron, L. Gagnon, P . Nadeau, H. Spink, and V . Tewari. The quasisymmetric flag variety: a toric complex on noncrossing partitions, 2025, 2508.12171. 2, 11
arXiv 2025
-
[6]
Bergeron and F
N. Bergeron and F. Sottile. Schubert polynomials, the Bruhat order, and the geometry of flag manifolds.Duke Math. J., 95(2):373–423, 1998. 2, 13
1998
-
[7]
I. N. Bernšte ˘ın, I. M. Gelfand, and S. I. Gelfand. Schubert cells, and the cohomology of the spacesG/P.Uspehi Mat. Nauk, 28(3(171)):3–26, 1973. 22
1973
-
[8]
S. C. Billey, Y. Gao, and B. Pawlowski. Introduction to the cohomology of the flag variety, 2025, 2506.21064. 20 RICHARDSON TABLEAUX AND SCHUBERT POSITIVITY 25
arXiv 2025
Show all 50 references
-
[9]
Björner and F
A. Björner and F. Brenti. An improved tableau criterion for Bruhat order.Electron. J. Combin., 3(1):Research Paper 22, approx. 5 pp, 1996. 4
1996
-
[10]
Björner and F
A. Björner and F. Brenti.Combinatorics of Coxeter groups, volume 231 ofGraduate Texts in Mathematics. Springer, New York, 2005. 4
2005
-
[11]
A. Borel. Sur la cohomologie des espaces fibrés principaux et des espaces homogènes de groupes de Lie compacts. Ann. of Math. (2), 57:115–207, 1953. 20
1953
-
[12]
E. Delanoy. Completely compressible Bruhat intervals and Kazhdan-Lusztig polynomials.European J. Combin., 29(3):746–759, 2008. 4
2008
-
[13]
V . V . Deodhar. Local Poincaré duality and nonsingularity of Schubert varieties.Comm. Algebra, 13(6):1379–1388,
-
[14]
Develin, J.L
M. Develin, J.L. Martin, and V . Reiner. Classification of Ding’s Schubert varieties: finer rook equivalence.Canad. J. Math., 59(1):36–62, 2007. 23
2007
-
[15]
K. Ding. Rook placements and cellular decomposition of partition varieties.Discrete Math., 170(1-3):107–151, 1997. 23
1997
-
[16]
du Cloux
F. du Cloux. An abstract model for Bruhat intervals.European J. Combin., 21(2):197–222, 2000. 4
2000
-
[17]
Fulton.Young tableaux, volume 35 ofLondon Mathematical Society Student Texts
W. Fulton.Young tableaux, volume 35 ofLondon Mathematical Society Student Texts. Cambridge University Press, Cambridge, 1997. With applications to representation theory and geometry. 3
1997
-
[18]
Gao and H
Y. Gao and H. Zhu. Boolean Schubert Structure Coefficients, 2025, 2405.05527. 2
2025
-
[19]
Graham and R
W. Graham and R. Zierau. Smooth components of Springer fibers.Ann. Inst. Fourier (Grenoble), 61(5):2139–2182 (2012), 2011. 19
2012
-
[20]
J. J. Güemes. On the homology classes for the components of some fibres of Springer’s resolution.Astérisque, (173- 174):10, 257–269, 1989. 2, 19
1989
-
[21]
D. Huang. Schubert products for permutations with separated descents.Int. Math. Res. Not. IMRN, (20):17461– 17493, 2023. 2
2023
-
[22]
Huang and P
D. Huang and P . Pylyavskyy. Bumpless pipe dream RSK, growth diagrams, and Schubert structure constants, 2022, 2206.14351. 2
2022 arXiv
-
[23]
Josuat-Vergès and J
M. Josuat-Vergès and J. S. Kim. Generalized Dyck tilings.European J. Combin., 51:458–474, 2016. 7, 8
2016
-
[24]
S. N. Karp and M. E. Precup. Richardson tableaux and components of Springer fibers equal to Richardson varieties, 2025, 2506.20792. 1, 2, 15, 18, 19, 22
2025 arXiv
-
[25]
D. E. Knuth.The art of computer programming. Vol. 1: Fundamental algorithms. Addison-Wesley Publishing Co., Read- ing, Mass.-London-Don Mills, Ont., 1969. Second printing. 5
1969
-
[26]
A. Knutson. Descent-cycling in Schubert calculus.Experiment. Math., 10(3):345–353, 2001. 14
2001
-
[27]
Knutson and T
A. Knutson and T. Tao. The honeycomb model ofGL n(C)tensor products. I. Proof of the saturation conjecture.J. Amer. Math. Soc., 12(4):1055–1090, 1999. 2
1999
-
[28]
Knutson and P
A. Knutson and P . Zinn-Justin. Schubert puzzles and integrability iii: separated descents, 2023, 2306.13855. 2
2023 arXiv
-
[29]
Lascoux and M.-P
A. Lascoux and M.-P . Schützenberger. Polynômes de Schubert.C. R. Acad. Sci. Paris Sér. I Math., 294(13):447–450,
-
[30]
D. E. Littlewood.The Theory of Group Characters and Matrix Representations of Groups. Oxford University Press, New York, 1940. 2
1940
-
[31]
Loday and M
J.-L. Loday and M. O. Ronco. Hopf algebra of the planar binary trees.Adv. Math., 139(2):293–309, 1998. 10
1998
-
[32]
Loday and M
J.-L. Loday and M. O. Ronco. Order structure on the algebra of permutations and of planar binary trees.J. Algebraic Combin., 15(3):253–270, 2002. 10
2002
-
[33]
G. Lusztig. Total positivity in Springer fibres.Q. J. Math., 72(1-2):31–49, 2021. 2 26 HUNTER SPINK AND VASU TEWARI
2021
-
[34]
Nadeau, H
P . Nadeau, H. Spink, and V . Tewari. The geometry of quasisymmetric coinvariants, 2024, 2410.12643. 2, 7, 11, 14, 22
2024 arXiv
-
[35]
Nadeau, H
P . Nadeau, H. Spink, and V . Tewari. Quasisymmetric divided differences, 2024, 2406.01510. 2
2024
-
[36]
Pak and C
I. Pak and C. Robichaux. Signed puzzles for Schubert coefficients, 2025, 2504.17734. 2
2025 arXiv
-
[37]
Pak and C
I. Pak and C. Robichaux. Vanishing of Schubert coefficients via the effective Hilbert nullstellensatz.Forum Math. Sigma, 13:Paper No. e162, 2025. 2
2025
-
[38]
Pechenik and A
O. Pechenik and A. Weigandt. An inverse Grassmannian Littlewood-Richardson rule and extensions.Forum Math. Sigma, 12:Paper No. e114, 24 pp, 2024. 2
2024
-
[39]
M. P . Schützenberger. Quelques remarques sur une construction de Schensted.Math. Scand., 12:117–128, 1963. 3
1963
-
[40]
Schützenberger
M.-P . Schützenberger. La correspondance de Robinson. InCombinatoire et représentation du groupe symétrique (Actes Table Ronde CNRS, Univ. Louis-Pasteur Strasbourg, Strasbourg, 1976), Lecture Notes in Math., Vol. 579, pages 59–113. Springer, Berlin-New York, 1977. 2
1976
-
[41]
N. J. A. Sloane. The encyclopedia of integer sequences. 24
-
[42]
F. Sottile. Pieri’s formula for flag manifolds and Schubert polynomials.Ann. Inst. Fourier (Grenoble), 46(1):89–110,
-
[43]
Spaltenstein
N. Spaltenstein. The fixed point set of a unipotent transformation on the flag manifold.Indag. Math., 38(5):452–456,
-
[44]
T. A. Springer. The unipotent variety of a semi-simple group. InAlgebraic Geometry (Internat. Colloq., Tata Inst. Fund. Res., Bombay, 1968), volume 4 ofTata Inst. Fundam. Res. Stud. Math., pages 373–391. Tata Inst. Fund. Res., Bombay,
1968
-
[45]
T. A. Springer. Trigonometric sums, Green functions of finite groups and representations of Weyl groups.Invent. Math., 36:173–207, 1976. 1
1976
-
[46]
R. P . Stanley.Enumerative combinatorics. Vol. 1, volume 49 ofCambridge Studies in Advanced Mathematics. Cambridge University Press, Cambridge, 1997. With a foreword by Gian-Carlo Rota, Corrected reprint of the 1986 original. 10
1997
-
[47]
R. P . Stanley.Enumerative combinatorics. Vol. 2, volume 62 ofCambridge Studies in Advanced Mathematics. Cambridge University Press, Cambridge, 1999. With a foreword by Gian-Carlo Rota and appendix 1 by Sergey Fomin. 3
1999
-
[48]
R. P . Stanley. Positivity problems and conjectures in algebraic combinatorics. InMathematics: frontiers and perspec- tives, pages 295–319. Amer. Math. Soc., Providence, RI, 2000. 1
2000
-
[49]
Woo and A
A. Woo and A. Yong. Schubert geometry and combinatorics, 2023, 2303.01436. 20 DEPARTMENT OFMATHEMATICS, UNIVERSITY OFTORONTO, TORONTO, ON M5S 2E4, CANADA Email address:hunter.spink@utoronto.ca DEPARTMENT OFMATHEMATICAL ANDCOMPUTATIONALSCIENCES, UNIVERSITY OFTORONTOMISSISSAUGA,...
2023 arXiv
-
[1976]
Nederl. Akad. Wetensch. Proc. Ser. A79. 1
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