REVIEW 3 major objections 4 minor 41 references
Sign-patterns of Certain Infinite Products
T0 review · 3 major / 4 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read For every prime p>3 and integer i>1 not divisible by p, the coefficients of (q^i;q^i)_∞/(q^p;q^p)_∞ are eventually periodic in sign modulo p, with an explicit threshold; the case (p,i)=(5,2) proves a conjecture from [9].
desk verdict Genuinely new sign-pattern results that resolve Bringmann et al. conjectures, but the central dissection formula is imported from the authors' unpublished preprint and needs to be proved in the paper. 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 carrying mechanism is the $m$-dissection formula for the quintuple product (Theorem 2.1), taken from [22]. It splits the product $(q^j,q^{M-j},q^M;q^M)_\infty(q^{M-2j},q^{M+2j};q^{2M})_\infty$ into a finite signed sum with exponents $L(r)=6r^2+\cdots$ and with each summand a product whose ordinary power series has nonnegative coefficients. Setting $M=4$, $j=1$ turns this into a $p$-dissection of $(q;q)_\infty$ (Corollary 2.1), in which the sign of the $r$-th summand is $(-1)^{s(r)}$ and $s(r)$ takes the values $0,1,2$ according to the same thresholds on $r$. After replacing $q$ by $q^i$ and dividing by $(q^p;q^p)_\infty$, only summands whose exponent $iL(r)$ lies in a given residue class contribute to $a_n$, and Lemma 2.1 shows those contributions are strictly positive or negative eventually. Consistency of the sign within each residue class follows from the symmetry of the quadratic $6r^2+r$ modulo $p$: for $p\equiv 1 \pmod 3$, the two outer ranges of $r$ are interchanged by $r+r'\equiv (p-1)/6 \pmod p$, and the case $p\equiv -1 \pmod 3$ is analogous.
What would settle it
Expand both sides of Theorem 2.1 for $M=4$, $j=1$, and $m=5$ as power series in $q$ to order $q^{60}$; if the sides disagree, the load-bearing dissection is false. Equivalently, directly expand $(q^2;q^2)_\infty/(q^5;q^5)_\infty$: a nonzero coefficient with $n\equiv 1$ or $3 \pmod 5$, or a coefficient that is not positive when $n\equiv 0 \pmod 5$, would disprove the theorem's corollary.
Extended reading notes
Core claim
On the paper's own terms, the central result is Theorem 1.1. Let $f_j=(q^j;q^j)_\infty$ and write $f_i/f_p=\sum_{n=0}^\infty a_n q^n$. For $p\equiv 1 \pmod 3$, define $L(r)$ piecewise with breakpoints $(4p-1)/12$ and $(10p-1)/12$; for $p\equiv -1 \pmod 3$, the breakpoints are $(2p-1)/12$ and $(8p-1)/12$. Then for every $n>N(p,i)$, where $N(p,i)$ is the maximum, over residue classes $s \pmod p$, of the least value of $iL(r)$ congruent to $s$, the paper proves $a_n>0$ when $n\equiv i(6r^2+r) \pmod p$ with $r$ in the outer intervals, $a_n<0$ in the inner interval, and $a_n=0$ otherwise. Corollary 1.1 is the case $(p,i)=(5,2)$: the coefficients of $(q^2;q^2)_\infty/(q^5;q^5)_\infty$ are positive exactly for $n\equiv 0 \pmod 5$, negative for $n\equiv 2,4 \pmod 5$, and zero for $n\equiv 1,3 \pmod 5$, for every $n\ge 0$. Theorem 1.2 extends the same sign analysis to other eta quotients, including $(q;q)^9/(q^3;q^3)^9$ with period-9 signs and several cases in the table from [9].
Load-bearing premise
Everything rests on an unproved dissection identity quoted from the authors' earlier preprint [22]: the quintuple product can be split into a signed finite sum whose pieces have nonnegative coefficients, and if that identity is false, the $p$-dissection of $(q;q)_\infty$ and the resulting sign patterns do not follow.
Editorial extensions
If this is right
- For every prime $p>3$ and every integer $i>1$ not divisible by $p$, the coefficients of $(q^i;q^i)_\infty/(q^p;q^p)_\infty$ are ultimately periodic in sign with period $p$, and the threshold $N(p,i)$ is explicit.
- The case $(p,i)=(5,2)$ settles the conjecture $C215^{-1}$ from [9] in full: $a_n>0$ for $n\equiv 0 \pmod 5$, $a_n<0$ for $n\equiv 2,4 \pmod 5$, and $a_n=0$ otherwise.
- Theorem 1.2 proves the specific sign patterns listed for the entries $5/++0+0$, $4/+-00$, $3/+0-$, $4/+-+0$, $4/+++0$, $5/+- - ++$, and $9/+-+--+0-+$ in the table from [9].
- Whenever $\gcd(t,6)=1$, Corollary 2.1 yields a $t$-dissection of $(q;q)_\infty$, so the same method can be applied to quotients such as $(q^j;q^j)^m/(q^t;q^t)$ and $(q^j;q^j)^m/(q^t;q^t)^m$, although the dissections may then be sums of products with mixed signs.
Reading between the lines
- An unstated consequence is that the proof strategy is algorithmic: for any fixed $(p,i)$, the bound $N(p,i)$ is computable, so the eventual sign pattern can be verified by checking only finitely many coefficients.
- A testable extension of the same dissection idea would be to rational powers of the product $(q;q)_\infty/(q^p;q^p)_\infty$; numerical experiments for small $p$ could reveal which residue classes remain single-signed and which develop mixed signs.
- The paper's own table of coefficient counts for two unproven quotients suggests that for some residue classes the coefficients may never become single-signed; if that persists, an eventual sign-periodicity statement for those classes would need a weaker formulation than pure $+$ or $-$.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies the sign patterns of the Fourier coefficients of the eta quotient (q^i;q^i)_∞/(q^p;q^p)_∞ for primes p>3 and integers i>1 with p∤i. Theorem 1.1 asserts that, for n larger than an explicit bound N(p,i), the sign of the coefficient an is determined entirely by n mod p: the positive, negative, and zero residues are specified in terms of the quadratic L(r)=6r^2+r and the residue of p modulo 3. Corollary 1.1 specializes this to (p,i)=(5,2) and thereby proves a conjecture of Bringmann et al. (C215^-1). Theorem 1.2 gives sign-periodicity results for ten further eta quotients, several of which address other conjectures from the same source. The proofs are based on m-dissections, a quintuple-product dissection formula, theta-function identifications, and a lemma asserting that certain quotients of infinite products have nonnegative coefficients.
Significance. If the main results are correct, the paper provides a uniform method for determining sign patterns of a natural family of eta quotients and proves several open conjectures from the Bringmann et al. program, including the previously conjectured sign pattern for (q^2;q^2)_∞/(q^5;q^5)_∞. The explicit N(p,i) bounds and the sharpness table are also useful. However, the central theorem depends on an unproved m-dissection formula quoted from the authors' own unpublished preprint, and the statement of N(p,i) is formally ill-defined for some (p,i); these issues must be addressed before the results can be considered fully established. The paper does not provide machine-checked proofs, but the small cases (p,i)=(5,2) and (7,2) are consistent with the stated patterns.
major comments (3)
- [Section 2.1, Theorem 2.1] Theorem 2.1, the m-dissection formula for the quintuple product, is quoted from reference [22], an unpublished preprint by three of the authors, and is not proved in this manuscript. This formula is the sole source of Corollary 2.1, which is then used in every step of the proof of Theorem 1.1 in Section 3. Since a sign or exponent error in s(r) or L(r) would change the claimed positive/negative/zero classification, the main theorem is currently contingent on an unverified black box. The authors should either provide a complete proof of Theorem 2.1 in an appendix or replace [22] with a published source that the reader can check.
- [Theorem 1.1, definition of N] The definition N = max(∪_{s=0}^{p-1} min{iL(r) : iL(r) ≡ s (mod p), 0 ≤ r ≤ p−1}) − p is not well-formed, because for some (p,i) the set over which min is taken is empty. For example, when (p,i)=(5,2), the residues 1 and 3 modulo 5 are not represented by iL(r) for any r, so min over an empty set is undefined and N is undefined. The statement can be repaired by taking the maximum only over nonempty residue classes (or by defining min(∅)=+∞), but as written the theorem is not formally meaningful for all admissible (p,i).
- [Section 3, proof of Theorem 1.1] The proof asserts without detail that the quantities t1(r), 4p^2−t1(r), 4p^2, 4p^2+t1(r), 8p^2−t1(r), 8p^2, t2(r), and 8p^2−t2(r) are pairwise distinct and all multiples of p. This verification is load-bearing: it is exactly what ensures that after division by (q^p;q^p)_∞ each numerator factor (1−q^{iα}) cancels a distinct factor of the denominator, so that the remaining series has nonnegative coefficients and the sign of each term is governed by (−1)^{s(r)}. The authors should provide the omitted verification for both cases p≡1 (mod 3) and p≡−1 (mod 3), including a demonstration that no overlap occurs between the arithmetic progressions generated by the different factors.
minor comments (4)
- [Title and Abstract] The title contains a spacing artifact ('P A TTERNS') that should be corrected, and the abstract can be made more precise about the scope of the 'additional classes' covered by Theorem 1.2.
- [References] Reference [3] contains a typo, 'Ramunujan' instead of 'Ramanujan'; reference [22] is an unpublished preprint whose status should be updated if it has appeared.
- [Section 4, proof of Theorem 1.2(5)] In the proof of part (5), the congruence argument 'if n1^2+m1^2 ≡ n2^2+m2^2 (mod 4), then (n1+n2)(n1−n2) ≡ (m1+m2)(m1−m2) (mod 2)' is not written correctly; the left- and right-hand sides should both involve differences (n1−n2) and (m1−m2). The intended conclusion about parity is likely correct, but the displayed line needs correction.
- [Theorem 1.2(2)] Part (2) states 'For p = 1 or an odd prime'; the case p=1 should be separated from the prime case for clarity, since p=1 is not prime.
Circularity Check
No circularity: the main sign pattern is derived from a general dissection identity, and the self-cited Theorem 2.1 is parameter-free and independent of the target result.
full rationale
Theorem 1.1 is not assumed anywhere in the paper; it is deduced from a p-dissection of (q;q)_infinity obtained in Corollary 2.1 by substituting M=4, j=1 into Theorem 2.1. The sign pattern emerges only after specializing that dissection and applying Lemma 2.1 to products with nonnegative coefficients, so the conclusion is not equivalent by construction to any input. The main provenance concern is that Theorem 2.1 is quoted from the authors' unpublished preprint [22] and not proved in the paper; however, this is a general quintuple-product dissection identity whose assumptions do not include the target sign pattern and which contains no fitted parameters, so under the stated rules it is independent support and does not constitute circularity. The remaining derivations rest on standard external identities (Borwein cubic theta functions, Ramanujan dissections, Cohen-Stromberg theta identities) and elementary coefficient-positivity lemmas. The formally problematic definition of N(p,i) using minima over possibly empty residue classes in Theorem 1.1 is a well-definedness and correctness issue, not a circularity. Overall, no equation in the paper reduces to its own input by construction, so the circularity score is 0.
Assumptions & free parameters
assumptions (5)
- ad hoc to paper Theorem 2.1: m-dissection formula for the quintuple product, quoted from [22]
- standard math Lemma 2.1: quotient of products expands with nonnegative coefficients
- standard math Jacobi triple product and theta identities (2.6)-(2.9)
- standard math Borwein cubic theta function identities (2.4) and Ramanujan's 5-dissection of (q;q)
- domain assumption Pairwise distinctness of exponents t1(r), t2(r), 4p^2-t1(r), 8p^2-t2(r), etc. within each dissection term
Cite this review
Pith. "Pith review of Sign-patterns of Certain Infinite Products." pith.science (2026). https://pith.science/paper/DZJNZ2KK
@misc{pith2026250716644,
author = {Pith},
title = {Pith review of: Sign-patterns of Certain Infinite Products},
year = {2026},
howpublished = {\url{https://pith.science/paper/DZJNZ2KK}},
note = {Machine review of arXiv:2507.16644}
}
abstract
The signs of Fourier coefficients of certain eta quotients are determined by dissecting expansions for theta functions and by applying a general dissection formula for certain classes of quintuple products. A characterization is given for the coefficient sign patterns for \[ \frac{(q^i;q^i)_{\infty}}{(q^p;q^p)_{\infty}} \] for integers \( i > 1 \) and primes \( p > 3 \). The sign analysis for this quotient addresses and extends a conjecture of Bringmann et al. for the coefficients of \( (q^2;q^2)_{\infty}(q^5;q^5)_{\infty}^{-1} \). The sign distribution for additional classes of eta quotients is considered. This addresses multiple conjectures posed by Bringmann et al.
Reference graph
Works this paper leans on
-
[22]
Dissection of the quintuple product, with applications , preprint
Huber, T.; McLaughlin, J.; Ye, D. Dissection of the quintuple product, with applications , preprint
-
[1]
Vanishing coefficients in the expansion of products of Rogers-Ramanujan type
Alladi, K.; Gordon B. Vanishing coefficients in the expansion of products of Rogers-Ramanujan type. Proc. Rademacher Centenary Conference, (G. E. Andrews and D. Bressoud, Eds.), Contemp. Math. 166, (1994), 129–139
work page 1994
-
[2]
On a Conjecture of Peter Borwein , Journal of Symbolic Computation, Volume 20, Issues 5–6, 1995
Andrews, G.E. On a Conjecture of Peter Borwein , Journal of Symbolic Computation, Volume 20, Issues 5–6, 1995
work page 1995
-
[3]
Andrews, G. E. Ramunujan’s “lost” notebook. III. The Rogers-Ramanujan continued fraction. Adv. in Math. 41 (1981), no. 2, 186–208
work page 1981
-
[4]
Andrews, G. E.; Bressoud, D. M. Vanishing coefficients in infinite product expansions. J. Austral. Math. Soc. Ser. A 27 (1979), no. 2, 199—202
work page 1979
-
[5]
N.D. Baruah and M. Kaur, Some results on vanishing coefficients in infinite product expansions . Ramanujan J. 53 (2020), no. 3, 551–568
work page 2020
-
[6]
Bringmann, K.; Heim, B.; Kane, B.; On a sign-change conjecture of Schlosser and Zhou, Journal of Mathematical Analysis and Applications, Volume 548, Issue 2, 2025
work page 2025
-
[7]
Sign changes of Fourier coefficients for holomorphic eta-quotients , preprint
Bringmann, K.; Han, G.; Heim, B.; Kane, B. Sign changes of Fourier coefficients for holomorphic eta-quotients , preprint
Show all 41 references
-
[8]
Vanishing properties of Fourier coefficients of holomorphic η- quotients, preprint
Bringmann, K.; Han, G.; Heim, B.; Kane, B. Vanishing properties of Fourier coefficients of holomorphic η- quotients, preprint
-
[9]
Periodic sign changes of weakly holomorphic η-quotients, preprint
Bringmann, K.; Han, G.; Heim, B.; Kane, B. Periodic sign changes of weakly holomorphic η-quotients, preprint
-
[10]
On a generalization of vanishing coefficients in two q-series expansions
Channabasavayya; Dasappa, R. On a generalization of vanishing coefficients in two q-series expansions. J. Ramanujan Math. Soc. 39 (2024), no. 2, 187–192
2024
-
[11]
K.; Dasappa, R
Channabasavayya; Keerthana, G. K.; Dasappa, R. On a generalization of 5-dissections of some infinite q- products. Ramanujan J. 64 (2024), no. 4, 1335–1355
2024
-
[12]
Vanishing coefficients in quotients of theta functions of modulus five
Chern, S.; Tang, D. Vanishing coefficients in quotients of theta functions of modulus five. Bull. Aust. Math. Soc. 102 (2020), no. 3, 387–398
2020
-
[13]
5-dissections and sign patterns of Ramanujan ’s parameter and its companion
Chern, S.; Tang, D. 5-dissections and sign patterns of Ramanujan ’s parameter and its companion. Czechoslovak Math. J. 71(146) (2021), no. 4, 1115–1128
2021
-
[14]
General coefficient-vanishing results associated with theta series
Chern, S.; Tang, D. General coefficient-vanishing results associated with theta series. Adv. in Appl. Math. 159 (2024), Paper No. 102742, 66 pp
2024
-
[15]
Modular forms: A classical approach , Graduate Studies in Mathematics, Vol 179, Amer
Cohen, H.; Str¨ omberg, F. Modular forms: A classical approach , Graduate Studies in Mathematics, Vol 179, Amer. Math. Soc., Providence, 2017
2017
-
[16]
Ramanujan ’s theta functions, Springer, Cham, 2017
Cooper, S. Ramanujan ’s theta functions, Springer, Cham, 2017
2017
-
[17]
Vanishing coefficients in two q-series related to Legendre-signed partitions
Daniels, T. Vanishing coefficients in two q-series related to Legendre-signed partitions. Res. Number Theory 10 (2024), no. 4, Paper No. 81, 12 pp
2024
-
[18]
Dou, D. Q. J.; Xiao, J. The 5-dissections of two infinite product expansions. Ramanujan J. 54 (2021), no. 3, 475–484
2021
-
[19]
Collected Papers of Srinivasa Ramanujan (AMS Chelsea, Provi- dence, 2000)
Hardy, G.H.; Seshu Aiyar, P.V.; Wilson, B.M. Collected Papers of Srinivasa Ramanujan (AMS Chelsea, Provi- dence, 2000)
2000
-
[20]
Hirschhorn, M. D. On the expansion of Ramanujan ’s continued fraction, Ramanujan J. 2 (1998), no. 4, 521–527
1998
-
[21]
Hirschhorn, M. D. Two remarkable q-series expansions. Ramanujan J. 49(2019), no. 2, pp 451–463
2019
-
[23]
Results on vanishing coefficients in infinite q-series expansions for certain arithmetic progres- sions mod7
Kaur, M.; Vanda. Results on vanishing coefficients in infinite q-series expansions for certain arithmetic progres- sions mod7. Ramanujan J. 58 (2022), no. 1, 269–289
2022
-
[24]
On the vanishing coefficients of odd powers of Ramanujan ’s theta functions
Liu, J.-C. On the vanishing coefficients of odd powers of Ramanujan ’s theta functions. Ramanujan J. 65 (2024), no. 1, 45–2
2024
-
[25]
Further results on vanishing coefficients in infinite product expansions , J
Mc Laughlin, J. Further results on vanishing coefficients in infinite product expansions , J. Aust. Math. Soc. 98 (2015), no. 1, 69–77
2015
-
[26]
New infinite q-product expansions with vanishing coefficients
Mc Laughlin, J. New infinite q-product expansions with vanishing coefficients. Ramanujan J 55, 733–760 (2021). https://doi.org/10.1007/s11139-020-00275-w 18
2021 doi
-
[27]
m-Dissections of some infinite products and related identities , The Ramanujan Journal (2022) 59:313–350
McLaughlin, J. m-Dissections of some infinite products and related identities , The Ramanujan Journal (2022) 59:313–350
2022
-
[28]
Further results on Vanishing Coefficients in infinite products of the form (qb, qp−b; qp)3 ∞(qjb, q2p−jb; q2p)∞ Int
Mc Laughlin, J.; Zimmer P. Further results on Vanishing Coefficients in infinite products of the form (qb, qp−b; qp)3 ∞(qjb, q2p−jb; q2p)∞ Int. J. Number Theory 18 (2022), no. 8, 1863–1885
2022
-
[29]
Theta-function identities of Ramanujan ’s continued fractions of order fourteen and twenty-eight, partition identities and vanishing coefficients
Rajkhowa, S.; Saikia, N. Theta-function identities of Ramanujan ’s continued fractions of order fourteen and twenty-eight, partition identities and vanishing coefficients. Funct. Approx. Comment. Math. 70 (2024), no. 2, 233–244
2024
-
[30]
The Taylor coefficients of certain infinite products
Richmond, B.; Szekeres, G. The Taylor coefficients of certain infinite products. Acta Sci. Math. (Szeged) 40 (1978), no. 3–4, 347—369
1978
-
[31]
J.; Zhou, N
Schlosser, M. J.; Zhou, N. H. On the infinite Borwein product raised to a positive real power. Ramanujan J. 61 (2023), no. 2, 515–543
2023
-
[32]
D.; Thulasi, M
Somashekara, D. D.; Thulasi, M. B. Results on vanishing coefficients in certain infinite q-series expansions. Ramanujan J. 60 (2023), no. 2, 355–369
2023
-
[33]
Vanishing coefficients in some q-series expansions
Tang, D. Vanishing coefficients in some q-series expansions. Int. J. Number Theory 15 (2019), no. 4, 763–773
2019
-
[34]
Vanishing coefficients on four quotients of infinite product expansions
Tang, D. Vanishing coefficients on four quotients of infinite product expansions. Bull. Aust. Math. Soc. 100 (2019), no. 2, 216–224
2019
-
[35]
On 5- and 10-dissections for some infinite products
Tang, D. On 5- and 10-dissections for some infinite products. Ramanujan J. 56 (2021), no. 2, 425–450
2021
-
[36]
Vanishing coefficients in three families of products of theta functions
Tang, D. Vanishing coefficients in three families of products of theta functions. Rev. R. Acad. Cienc. Exactas F ´ ıs. Nat. Ser. A Mat. RACSAM117 (2023), no. 1, Paper No. 36, 11 pp
2023
-
[37]
Vanishing coefficients in three families of products of theta functions
Tang, D. Vanishing coefficients in three families of products of theta functions. II. Results Math. 78 (2023), no. 4, Paper No. 124, 28 pp
2023
-
[38]
Vanishing coefficients in powers of theta functions with odd moduli
Tang, D. Vanishing coefficients in powers of theta functions with odd moduli. Rocky Mountain J. Math. 54 (2024), no. 1, 261–267
2024
-
[39]
Vanishing coefficients of q5n+r and q11n+r in certain infinite q-product expansions
Vanda; Kaur, M. Vanishing coefficients of q5n+r and q11n+r in certain infinite q-product expansions. Ann. Comb. 26 (2022), no. 3, 533–557
2022
-
[40]
Sign changes of coefficients of powers of the infinite Borwein product
Wang, L. Sign changes of coefficients of powers of the infinite Borwein product. Adv. in Appl. Math. 141 (2022), Paper No. 102405, 31 pp
2022
-
[41]
Xia, E. X. W.; Zhao, A. X. H. Generalizations of Hirschhorn ’s results on two remarkable q-series expansions, Exp. Math. 31 (2022), no. 3, 878–882. School of Mathematics (Zhuhai), Sun Yat-sen University, Zhuhai 519082, Guangdong, People’s Re- public of China Email address : hu...
2022
Reviewed August 6, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.