REVIEW 3 major objections 4 minor 36 references
In Search of Homology for Quasigroups of Bol-Moufang Type
T0 review · 3 major / 4 minor · reviewed 2026-08-05 · deepseek-v4-flash
Pith's one-line read This paper constructs the first homology groups for quasigroups of Bol-Moufang type, defining boundary maps from extensions by affine quasigroups and computing H1 and H2 for the examples that distinguish all 26 varieties.
desk verdict New boundary maps give the first H1/H2 for Bol-Moufang quasigroups, but the key variety-independence conjecture is presented as 'checked' without a single same-variety comparison. 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 objects are the rooted binary tree polynomials $h(T)$, $H(T)$, and $Q(T)$. For a tree $T$ with ordered leaves, $h(T)$ records the path weights (words in $t$ and $s$) from the root to each internal vertex, $H(T)$ evaluates the tree as an affine word in the leaf labels $a_1, \ldots, a_n$, and $Q(T)$ records, for each internal vertex, the pair of subwords being multiplied, weighted by the path word. The boundary maps are defined by $\partial_2(x, y) = tx + sy - xy$ (obtained from equivalence of extensions) and $\partial_3(x, y, z) = Q(V^i) - Q(V^j)$ (obtained from the two trees in the Bol-Moufang identity $V^{ij}$). The proof that these form a chain complex uses the cancellation identity $\partial_2(Q(T)) = -\text{root word} + \text{sum of leaf terms}$, whose
What would settle it
Take the smallest quasigroup in the RG1L variety that satisfies both defining identities A25 and D25, compute $H_2(X; A25, 1, 1)$ and $H_2(X; D25, 1, 1)$, and compare the two abelian groups. If they are not isomorphic, Conjecture 6.1 is false. The paper's own data never performs this comparison for two identities that define the same variety, so this single computation would settle the central open claim.
Extended reading notes
Core claim
For any quasigroup $X$ of Bol-Moufang type and any admissible substitution $(t, s)$ of automorphisms of an abelian group, the sequence $0 \to kX^3 \xrightarrow{\partial_3} kX^2 \xrightarrow{\partial_2} kX \to 0$ is a chain complex, where $\partial_2(x, y) = tx + sy - xy$ and $\partial_3(x, y, z) = Q(V^i) - Q(V^j)$ for the defining identity $V^{ij}$. Here $Q$ is a polynomial associated to a rooted binary tree that records, for each internal vertex, the pair of subwords being multiplied and the path weights in $t$ and $s$. The paper verifies $\partial_2 \partial_3 = 0$ using the identity $\partial_2(Q(T)) = -\text{root word} + \text{sum of leaf terms}$, together with the previously determined affine solutions (List 3.9). This makes $H_1$ and $H_2$ well-defined for every Bol-Moufang quasigroup. The paper further shows t
Load-bearing premise
The claim that $H_2$ depends only on the variety, not on which defining identity is chosen, is supported only by the computed examples and not proved in general; if two identities defining the same variety gave different $H_2$, the table of homology by variety would lose its meaning.
Editorial extensions
If this is right
- Every quasigroup of Bol-Moufang type now has well-defined homology groups H₁ and H₂ for each admissible substitution (t, s), with H₁(X; 1, 1) the universal abelian quotient of X.
- The homology H₁ for the substitutions (1, −1) and (−1, 1) is the abelianization of the parastrophes (X, /) and (X, \), respectively, giving a homology-theoretic interpretation of parastrophe duality.
- If Conjecture 6.1 holds, H₂(X; Vⁱʲ, t, s) is an invariant of the variety membership of X rather than of the chosen defining identity, so one may speak of, for example, the 'RG1 homology' of a quasigroup.
- For groups, the conjecture predicts that any Bol-Moufang identity defining the variety of groups yields the usual group homology of X.
- The construction is deliberately low-dimensional (only ∂₂ and ∂₃); the paper leaves open the problem of defining higher boundary maps ∂ₙ for n ≥ 4.
Reading between the lines
- If variety invariance of H₂ is confirmed, the second homology could serve as a new tool for distinguishing quasigroup varieties from each other, complementing the equational-reasoning classification of Phillips and Vojtechovsky.
- The 'Alexander solution' t + s = 1 with c₀ = 0 that appears for the FQ0 varieties suggests a possible connection with knot-theoretic Alexander invariants and Yang-Baxter homology, where similar substitutions arise.
- The X14 identity (four distinct variables) gives a ∂₃ whose homology is always a common quotient of the H₂ groups computed from the repeated-letter identities Aij through Fij; this quotient could be used to detect how sensitive the homology is to repetition of variables.
- The small-category homology of the multiplication group (computed in Section 6.1) gives different invariants from the proposed Bol-Moufang homology, so the two theories capture genuinely different information about the same quasigroup.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a new (co)homology theory for quasigroups of Bol-Moufang type, based on extensions by affine quasigroups. The main construction defines a 3-term chain complex 0 → kX^3 --∂3--> kX^2 --∂2--> kX → 0, with ∂2(x,y)=tx+sy−xy and ∂3(x,y,z)=Q(T_i)−Q(T_j) for the Bol-Moufang identity V_ij. The authors verify ∂2∂3=0 in Section 4.1, prove that H1(X;1,1) is the universal abelian quotient of X, and compute H1 and H2 for the 19 distinguishing examples of Phillips and Vojtechovsky. They conjecture (Conjecture 6.1) that H2 depends only on the variety of quasigroups, not on the chosen defining identity, and they speculate about a connection to homology of small categories.
Significance. If correct, the paper provides the first systematic homology theory for Bol-Moufang quasigroups, with an explicit and computable chain complex. The construction is concrete: ∂2 is derived from equivalence of extensions, and ∂3 is defined directly from the bracketing trees, which makes the theory easy to apply. The verification of the chain complex condition is a genuine contribution, as is the interpretation of H1 as a form of abelianization, including the parastrophe cases. The extensive tables of H1 and H2 for the Phillips–Vojtechovsky examples are a useful resource. However, the central interpretive claim that H2 is a homology invariant of the variety, rather than of a quasigroup together with a chosen identity, rests on unproven Conjecture 6.1; the data presented in Section 5 do not actually test this conjecture, because no same-variety identity comparison is shown. This limits the significance of the per-variety tables until the conjecture is either proved or the presentation is restricted to the identity-specific results.
major comments (3)
- [List 3.9, items (12)(a) and (15)(a)] The statement that H2 is independent of the choice of defining identity within a variety is load-bearing for the organization of Section 5 and for phrases such as 'RG1 homology' in Section 6. The text says this is 'evidenced by the experimental data' (§3.4) and 'our data supports' (§5), but no displayed example compares two identities that define the same variety. Each listed quasigroup satisfies identities from distinct varieties; for instance, A1 in Example 5.1 satisfies A25, A23, B25, E25, A14, F25, C25, and A35, none of which are equivalent. To support the conjecture, one would need, e.g., a quasigroup satisfying both A25 and D25 (both RG1L) with equal H2 for the two ∂3 maps. As written, the per-variety H2 table is unsupported, and the phrase 'RG1 homology' is premature. Please either prove the conjecture, provide such same-variety comparisons, or explicitly mark all per-variety entr
- [List 3.9] List 3.9 contains visible errors that undermine the claim of determining the 'full set of solutions' (t,s) for every identity. In item (12)(a) (C15), the displayed h-value is h(E25), not h(C15). In item (15)(a) (A15), the solution set is listed as 's=1 and t^2+t=2', with the conclusion '(t,s)=(-2,1)'; the solution t=1 (which is always available) is omitted. Since the chain-complex verification in §4.1 relies on the completeness and correctness of these solution sets, the list must be corrected. I would also recommend that the derivation be supplemented by a computer-checkable table or script, given the number of cases.
- [List 3.9] The affine solution sets for all 26 varieties are summarized in List 3.9, but the derivation is carried out in detail only for the right Bol case (E25); the other 25 are said to be 'very similar' and 'left as an exercise'. Given that both the chain-complex verification and the per-variety homology calculations depend on these solution sets, this is a reproducibility gap. At minimum, the authors should include an appendix or supplementary file containing the full derivation for all cases, or a clear algorithmic description that allows the reader to verify each entry independently. The typo in C15 and the omission in A15 reinforce the need for such a check.
minor comments (4)
- [§3.4] The definition of H2 is written as 'H2(X; V_ij) = Im ∂3^{V_ij} / ker ∂2', which is inverted. The correct definition is ker ∂2 / Im ∂3^{V_ij}, as used in Section 5 and elsewhere. Please fix this typo.
- [§5] The table headers for Examples 5.7 and 5.19 read 'H2(A3; V_ij, t, s)', but the examples are for A7 and A19, respectively.
- [List 3.9] In the A15 entry, the expression for H(A15) appears to have a typo: the third coefficient is written as 's(s^2−1)c', while the surrounding analysis suggests it should involve t as well; please recheck.
- [§3.4] Notation is sometimes inconsistent, e.g., '(x, xy)t' appears where 't(x, xy)' is meant. A uniform convention for writing monomials in t and s would improve readability.
Circularity Check
No circular derivation: the chain complex and homology computations are self-contained; minor presentation issue: Conjecture 6.1 is used to organize per-variety tables without the same-variety comparisons that would support it.
-
other
[Section 3.4 (intro to the list of ∂3 maps), Section 5 (intro before Example 5.1), and Conjecture 6.1 in Section 6]
"As evidenced by the experimental data, H2(X; V ij) = Im ∂V ij 3 / ker ∂2 ∼= Im ∂W kℓ 3 / ker ∂2 = H2(X; W kℓ) if V ij and W kℓ define the same variety of quasigroups; see Conjecture 6.1. Consequently the list of boundary maps that follows is organized according to the 26 equational classes (varieties) of BMq's. ... Consistent with Conjecture 6.1, our data supports H2(X, V ij, t, s) = H2(X, W kℓ, t, s) if V ij and W kℓ define the same variety of Bol-Moufang quasigroup. Thus, we show only one computation H2(X, V ij, t, s) for V ij a given representative of a variety."
The per-variety organization of ∂3 and the Section 5 tables presupposes variety-invariance of H2: only one defining identity is used per variety, and Section 6 speaks of 'the RG1 homology.' The paper says this independence is 'evidenced by the experimental data' and 'consistent with Conjecture 6.1,' but no displayed computation compares two identities that define the same variety. Every quasigroup in Section 5 satisfies identities from distinct varieties (e.g., A1 satisfies A25, A23, B25, E25, A14, F25, C25, A35, none of which are equivalent). Thus the tables are organized by an unverified assumption presented as evidence; this is a circular-presentation/missing-support issue rather than a reduction of the homology values to their inputs.
full rationale
The central construction is not circular. ∂2(x,y)=tx+sy−xy is derived from equivalence of extensions (Proposition 3.4), and ∂3 is obtained from the cochain condition in the right Bol case and then defined generally as Q(V^i)−Q(V^j) (Definition 3.5, Section 3.4). The chain complex condition ∂2∂3=0 is verified directly in Lemma 4.1 and Corollary 4.2: the term −g(r1)+g(r2) vanishes because X satisfies the BM identity, and the remaining sum vanishes exactly for the affine (t,s) solutions tabulated in List 3.9. This is a direct computation, not an assumption of the conclusion. H1(X;1,1) as abelianization is proved by an adjunction argument (Proposition 4.3), and the H2 computations in Section 5 are explicit cokernel calculations. The only flagged weakness is Conjecture 6.1: the paper claims experimental support for H2 depending only on the variety, but no same-variety identity comparison is displayed, so the per-variety H2 tables and phrases like 'RG1 homology' rest on an unverified conjecture. This is a correctness/evidence gap, not a circular derivation. Minor typos in List 3.9 (e.g., h(E25) under C15; A15 omitting t=1 from the solution set despite (1,1) being used elsewhere) also deserve re-checking but do not affect the circularity assessment.
Assumptions & free parameters
free parameters (2)
- t =
per variety solution set (e.g., t=±1 for RBQL; t=-2,1 for LC3L)
- s =
per variety solution set (e.g., s=1 for RBQL; s=1 for LC3L)
assumptions (4)
- domain assumption t and s commute as scalar coefficients in the chain complex
- domain assumption The coefficient ring has no zero divisors in cases A14, B23, F25, C15
- domain assumption The classification of the 26 BMq varieties and the list of defining identities from Phillips-Vojtechovsky are correct
- standard math Standard algebraic facts: Birkhoff's HSP theorem, Bruck-Murdoch-Toyoda theorem, Eilenberg extension theory
Cite this review
Pith. "Pith review of In Search of Homology for Quasigroups of Bol-Moufang Type." pith.science (2026). https://pith.science/paper/XEHLMO76
@misc{pith2026250821268,
author = {Pith},
title = {Pith review of: In Search of Homology for Quasigroups of Bol-Moufang Type},
year = {2026},
howpublished = {\url{https://pith.science/paper/XEHLMO76}},
note = {Machine review of arXiv:2508.21268}
}
abstract
We initiate (co)homology theory for quasigroups of Bol-Moufang type based on analysis of their extensions by affine quasigroups of the same type. We use these extensions to define second and third boundary operations, $\partial_2(x,y)$ and $\partial_3(x,y,z)$, respectively. We use these definitions to compute the second homology groups for several examples from the work of Phillips and Vojtechovsky. We speculate about the relation between these homology groups and those obtained from a small category with coefficients in a functor.
Figures
Reference graph
Works this paper leans on
-
[1]
Clifford Bergman, Universal Algebra: Fundamentals and Selected Topics, Published by Taylor & Francis/CRC, 2011
work page 2011
-
[2]
G.M. Bergman, An Invitation to General Algebra and Universal Constructions (Universitext Book 351), Springer, Cham, 2015. x+572 pp
work page 2015
-
[3]
G. Bol, Gewebe und Gruppen, Math. Annalen , 114, 1937, No. 1, 414-431
work page 1937
-
[4]
R. H. Bruck, Some results in the theory of quasigroups, Trans. Amer. Math. Soc. vol. 55, 1944, pp. 19-52
work page 1944
- [5]
-
[6]
C. Chevalley, S. Eilenberg, Cohomology theory of Lie groups and Lie algebras, Trans. Amer. Math, Soc. , 63, 1948, 85-124
work page 1948
-
[7]
J.Duskin, Simplicial methods and interpretation of triple cohomology, Memoirs of AMS , 163, 1975
work page 1975
-
[8]
Eilenberg, Extensions of general algebras Ann
S. Eilenberg, Extensions of general algebras Ann. Soc. Polon. Math. 21 (1948), 125–134
work page 1948
Show all 36 references
-
[9]
Eilenberg, S
S. Eilenberg, S. Mac Lane, Cohomology theory in abstract groups, I, II, Annals of Math. 48, 1947, 51-78, 326-341
1947
-
[10]
Eilenberg, S
S. Eilenberg, S. Mac Lane, Algebraic cohomology groups and loops Duke Math. J. 14 (1947), 435–463
1947
-
[11]
Karpilovsky, The Schur Multipliers, Oxford Science Publications, London Mathematical society Monographs, New Series 2, Clarendon Press, Oxford, 1987, x+302 pp
G. Karpilovsky, The Schur Multipliers, Oxford Science Publications, London Mathematical society Monographs, New Series 2, Clarendon Press, Oxford, 1987, x+302 pp
1987
-
[12]
Algebra 183 (1996), no
Kenneth Kunen, Moufang quasigroups, J. Algebra 183 (1996), no. 1, 231–234
1996
-
[13]
Lebed, Braided objects: unifying algebraic structures and categorifying virtual braids December 2012, Thesis (Ph.D.), Universit\'e Paris 7
V. Lebed, Braided objects: unifying algebraic structures and categorifying virtual braids December 2012, Thesis (Ph.D.), Universit\'e Paris 7
2012
-
[14]
Lebed, Homologies of algebraic structures via braidings and quantum shuffles, J
V. Lebed, Homologies of algebraic structures via braidings and quantum shuffles, J. Algebra , 391, 2013, 152–192
2013
-
[15]
Lebed, abelian quandles and quandles with abelian structure group, e-print:\ arXiv:1908.06745 [math.GR]
V. Lebed, abelian quandles and quandles with abelian structure group, e-print:\ arXiv:1908.06745 [math.GR]
1908
-
[16]
Loday, Cyclic homology, Grund
J-L. Loday, Cyclic homology, Grund. Math. Wissen. Band 301, Springer-Verlag, Berlin, 1992 (second edition, 1998)
1992
-
[17]
Miller, The second homology of a group, Proc
C. Miller, The second homology of a group, Proc. Amer. Math. Soc. 3 (1952), 588-595
1952
-
[18]
Moufang, Zur Struktur der Alternativekoerpern, Math
R. Moufang, Zur Struktur der Alternativekoerpern, Math. Annalen , 110, 1935, 416-430
1935
-
[19]
D. C. Murdoch, Quasi-groups which satisfy certain generalized laws, American Journal of Math. , 16, 1939, pp. 509-522
1939
-
[20]
Niebrzydowski, J.H
M. Niebrzydowski, J.H. Przytycki, Entropic magmas, their homology, and related invariants of links and graphs, Algebraic & Geometric Topology (AGT) ,13(6), October 2013, 3223-3243;\\ e-print: \ arXiv:1211.2951 [math.GT]
2013 arXiv
-
[21]
Pflugfelder, Historical notes on loop theory, Commentationes Mathematicae Universitatis Carolinae , 41, 2000, 359-370
H.O. Pflugfelder, Historical notes on loop theory, Commentationes Mathematicae Universitatis Carolinae , 41, 2000, 359-370
2000
-
[22]
Pflugfelder, Quasigroups and Loops: Introduction, Sigma Series in Pure Mathematics, Heldermann, 1990
H.O. Pflugfelder, Quasigroups and Loops: Introduction, Sigma Series in Pure Mathematics, Heldermann, 1990
1990
-
[23]
Phillips, P
J.D. Phillips, P. Vojtechovsky, The varieties of quasigroups of Bol-Moufang type: an equational reasoning approach, Journal of Algebra , 293, 2005, 17-33
2005
-
[24]
Phillips, P
J.D. Phillips, P. Vojtechovsky, The varieties of loops of Bol-Moufang type, Algebra Universalis , 54, 2005, no. 3, 259–271
2005
-
[25]
Lebed, L
V. Lebed, L. Vendramin, Homology of left non-degenerate set-theoretic solutions to the Yang-Baxter equation, Adv. Math. , 304 (2017), 1219--1261; \\ e-print:\ arXiv:1509.07067 [math.QA]
2017 arXiv
-
[26]
J. H. Przytycki, Distributivity versus associativity in the homology theory of algebraic structures, Demonstratio Math. , 44(4), December 2011, 821-867; \\ e-print:\ http://front.math.ucdavis.edu/1109.4850
2011 arXiv
-
[27]
J. H. Przytycki, Knots and distributive homology: from arc colorings to Yang-Baxter homology, Chapter in: New Ideas in Low Dimensional Topology , World Scientific, Vol. 56, 413-488, 2015; e-print: \ arXiv:1409.7044 [math.GT]
2015 arXiv
-
[28]
Przytycki, J
J.H. Przytycki, J. Wang, Homology of small categories and Khovanov homology In the volume: Scientific Legacy of Professor Zbigniew Oziewicz, World Scientific, Vol 75 of Series on Knots and Everything, World Scientific Publishing Co. Pte. Ltd., Hackensack, NJ, 2023, 349-361
2023
-
[29]
Przytycki, X
J.H. Przytycki, X. Wang, Equivalence of two definitions of set-theoretic Yang-Baxter homology, Journal of Knot Theory and Its Ramifications , 27(7), June 2018, 1841013 (15 pages);\ e-print: \ arXiv:1611.01178 [math.GT]
2018 arXiv
-
[30]
Przytycki, X
J.H. Przytycki, X. Wang, The second Yang-Baxter homology for the Homflypt polynomial, Journal of Knot Theory and Its Ramifications , 30 (2021), no. 13, Paper No. 2141014, 14 pp.,\ e-print: \ arXiv:2004.07413 [math.GT]
2021 arXiv
-
[31]
Shcherbacov, Elements of quasigroup theory and applications, CRC Press, 2017
V. Shcherbacov, Elements of quasigroup theory and applications, CRC Press, 2017
2017
-
[32]
Smith, Mal'cev variety, Springer Lecture Notes in Mathematics, No.554, Springer-Verlag, Berlin, 1976
J.D.H. Smith, Mal'cev variety, Springer Lecture Notes in Mathematics, No.554, Springer-Verlag, Berlin, 1976
1976
-
[33]
Smith, An introduction to quasigroups and their representations
J.D.H. Smith, An introduction to quasigroups and their representations. Stud. Adv. Math. Chapman & Hall CRC, Boca Raton, FL, 2007. xii+340 pp
2007
-
[34]
Smith, Groups, triality, and hyperquasigroups, Journal of Pure and Applied Algebra , 216, 2012 811-825
J.D.H. Smith, Groups, triality, and hyperquasigroups, Journal of Pure and Applied Algebra , 216, 2012 811-825
2012
-
[35]
Toyoda, On affine geometry of abelian groups, Proceedings of the Imperial Academy , Volume 16(5), 1940, 161-164
K. Toyoda, On affine geometry of abelian groups, Proceedings of the Imperial Academy , Volume 16(5), 1940, 161-164
1940
-
[36]
C. E. Watts, A homology theory for small categories, In: Proc. of the Conf. on categorical algebra, La Jolla, Canada 1965
1965
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