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REVIEW 3 major objections 3 minor 34 references

Cusp forms as $p$-adic limits circumventing $p$-adic version of the Legendre period relation

T0 review · 3 major / 3 minor · reviewed 2026-08-07 · deepseek-v4-flash

Pith's one-line read The paper proves the p-adic constant γ is nonzero for all but finitely many supersingular primes, closing a gap in earlier constructions of cusp forms as p-adic limits.

desk verdict A genuinely new infinite-family non-vanishing result in p-adic mock modular form coupling, but the proof as written has sign errors and an unjustified strict isomorphism claim that need repair. read the letter →

arxiv 2506.07107 v2 pith:WO52OUCL submitted 2025-06-08 math.NT

classification math.NT MSC 11F1111F3314H52
keywords cuspformsp-adiclimitsmockmodularformalgrouplawssupersingularprimesGammafunctionellipticcurves
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper closes a gap in the program that expresses a cusp form as a $p$-adic limit of derivatives of harmonic Maass forms under repeated application of Atkin's $U$-operator. Earlier results in this direction required a certain constant $\gamma$ to be nonzero, and non-vanishing was known only in finitely many cases. The author proves that for a weight-2 newform with integer coefficients, $\gamma \neq 0$ for all but possibly finitely many supersingular primes $p$ with $b(p) = 0$, yielding an infinite family of examples. For the original example—the newform associated with the elliptic curve $y^2 = x^3 - x$—he computes $\gamma$ explicitly as a ratio of values of Morita's $p$-adic Gamma function (the $p$-adic analog of the classical Gamma function), making the non-vanishing transparent.

What carries the argument

The load-bearing object is the formal group law attached to the elliptic curve coming from the modular parametrization, together with its invariant differential. The quantity $\mu_p$ is defined by the condition that $\zeta(\Lambda, E_g) - \lambda_p E_g - \mu_p \frac{1}{p} E_g|V$ has a $p$-adically integral $q$-expansion, in direct analogy with the classical splitting of the Weierstrass zeta function. Honda's theorem gives a strict isomorphism over $\mathbb{Z}_p$ between this formal group and the one with logarithm $E_g$, and the paper introduces the $p$-typical formal group with logarithm $l_t(u) = \sum_{n \geq 0} (-1)^n \frac{u^{p^{2n}}}{p^n}$ to isolate the coefficient of $u^p$. That coefficient, multiplied by $p$, is congruent to $-\frac{1}{12} E_{p+1} \pmod{p}$; the second congruence is proved with Lang's factorization of Eisenstein polynomials into irreducibles over the algebraic closure of $\mathbb{F}_p$, showing $E_{p+1}$ cannot vanish modulo $p$ at a supersingular prime.

What would settle it

Take an elliptic curve with a supersingular prime of good reduction, for instance the curve $y^2 = 4x^3 + 16x$ at $p = 3$, and compute $\mu_p$ directly from the condition that $\zeta(\Lambda, E_g) - \lambda_p E_g - \mu_p \frac{1}{p} E_g|V$ has a $p$-adically integral $q$-expansion; if $\mu_p = 0$ for any such prime, Theorem 3 is false.

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Extended reading notes

Core claim

The central discovery is Theorem 1: under the setup described above, the exceptional $p$-adic constant $\gamma$ is nonzero for all but finitely many primes $p \nmid N$ with $b(p) = 0$. The proof passes through Theorem 3, which characterizes the $p$-adic quantity $\mu_p$ attached to the elliptic curve associated to $g$ via Eichler–Shimura theory: $\mu_p = 0$ if and only if the reduction at $p$ is ordinary. Since $b(p) = 0$ is exactly the supersingular case, this yields $\mu_p \neq 0$ and hence $\gamma \neq 0$. The argument reduces Theorem 3 to two congruences: $\mu_p \equiv -\frac{1}{12} E_{p+1} \pmod{p}$ and $E_{p+1} \not\equiv 0 \pmod{p}$ for primes of good supersingular reduction, proved using formal group laws and Lang's theory of Eisenstein polynomials. In the $N = 32$ example the paper further derives the explicit formula $\gamma = 8 \left(\frac{2}{p}\right) \frac{\Gamma_p(1/2)}{\Gamma_p(1/4)^2}$.

Load-bearing premise

The proof assumes, without proof, that the formal group law attached to the elliptic curve is strictly isomorphic over the $p$-adic integers to a particular standard height-2 formal group whose logarithm is the series $\sum_{n \geq 0} (-1)^n u^{p^{2n}}/p^n$.

Editorial extensions

If this is right

  • For any weight-2 newform with integer coefficients and infinitely many primes $p$ with $b(p)=0$, the $p$-adic limit in Proposition 1 converges to $g$ without any exceptional zero; the previously suspected obstruction $\gamma = 0$ occurs at most finitely often.
  • The non-vanishing is independent of one-dimensionality, complex multiplication, and eta-quotient presentations, so the result applies to an infinite family of cases rather than the finitely many covered by earlier methods.
  • The congruence $\mu_p \equiv -\frac{1}{12} E_{p+1} \pmod{p}$ ties the mock-modular coupling constant to the Eisenstein series $E_{p+1}$, making the relation between these $p$-adic limits and supersingular reduction explicit.
  • In the $N=32$ example, the explicit formula $\gamma = 8 \left(\frac{2}{p}\right) \frac{\Gamma_p(1/2)}{\Gamma_p(1/4)^2}$ gives a manifestly nonzero value for every $p \equiv 3 \pmod{4}$.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The proof only uses that the reduced formal group has height 2, not the finer structure of its isomorphism class; this suggests the same non-vanishing should hold for supersingular elliptic curves over number fields.
  • The explicit example produces $\mu_p^2$ where the classical complex period gives $\mu_\infty$ itself; this quadratic discrepancy hints at a deeper p-adic–complex period relation not explained in the paper, perhaps accessible through p-adic Chowla–Selberg theory.
  • A testable extension is to compute $\gamma$ via the congruence (11) for non-CM weight-2 newforms at supersingular primes; if any such computation produced $\gamma = 0$, the finite exception set in Theorem 1 would have to be made explicit.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 3 minor

Summary. The paper studies the non-vanishing of the p-adic constant γ that arises in recent results expressing a cusp form as a p-adic limit of weakly holomorphic modular forms under repeated Atkin U-operators. The author proposes a new approach: for a weight-2 newform g with b(p)=0, the exceptional constant γ is identified with a formal-group invariant µ_p of the associated elliptic curve, and the non-vanishing is reduced to a congruence µ_p ≡ -E_{p+1}/12 (mod p) together with a classical non-vanishing of E_{p+1} at supersingular primes. This yields Theorem 1, an infinite family of primes for which γ≠0, with an essentially uniform proof. The original example of El-Guindy and Ono (g=η^2(4τ)η^2(8τ), N=32) is treated in detail, and γ is computed explicitly in terms of Morita's p-adic Gamma function (Theorem 2). The proof combines Honda's formal group theorem, Dieudonné module invariants from the author's earlier work [13,14], and a coefficient-level calculation involving the Eisenstein series E_{p+1}.

Significance. If the main results are correct, the paper makes a genuine advance: it replaces the finitely many, CM-specific non-vanishing arguments of Ahlgren--Samart, Hanson--Jameson, and Dicks with a method that proves γ≠0 for all but finitely many supersingular primes in a general weight-2 setting, and it gives an explicit p-adic Gamma formula for the original N=32 example. The use of the Eisenstein series E_{p+1} as the source of non-vanishing is an appealing and potentially reusable idea. The paper also exhibits a clean connection between the mock-modular constant γ and Dieudonné-module invariants of the associated elliptic curve. However, several load-bearing points in the written proof are not correct as stated: an unjustified (and likely false) strict isomorphism claim in Section 4, a sign inconsistency between Theorem 2 and its proof, and an arithmetic error in the p=3 case. These issues do not destroy the plausibility of the main theorem, but they require substantial repair.

major comments (3)
  1. [Section 4, paragraph beginning "In order to prove Theorem 3"] The assertion that the formal group laws with logarithms Eg and l_t(u)=Σ(-1)^n u^{p^{2n}}/p^n are strictly isomorphic over Z_p whenever p is a prime of good reduction and b(p)=0 is not justified by the cited [16, Theorem 15.2.9]. Hazewinkel's theorem guarantees that every formal group over Z_p is strictly isomorphic to some p-typical formal group, but it does not identify the unit parameter of that p-typical group. For height-2 formal groups over Z_p, the strict isomorphism class is encoded in a unit modulo 1+pZ_p, and l_t corresponds to the parameter -1; a generic supersingular elliptic curve need not have this invariant. Since the subsequent computation of µ_p via ζ(Λ,l_t(u)) depends on this isomorphism, the proof of Theorem 3 has a real gap at this point. The gap is likely repairable: for any height-2 p-typical logarithm L(u)=u+O(u^p), the coefficient of u^p in ζ(Λ,L(u)) is still -2G_{p+1}/p! because 1/L has no u^p term and L(u)^p has u^p-coefficient 1, independent of the unit parameter. The paper should be revised to make this argument instead of claiming a specific strict isomorphism to l_t.
  2. [Theorem 2 and its proof in Section 3] There is a sign inconsistency between the theorem statement and the proof. Theorem 2 states γ = 8(2/p)Γ_p(1/2)/Γ_p(1/4)^2, while the proof concludes µ_p = -8(2/p)Γ_p(1/2)/Γ_p(1/4)^2. Since the author explicitly identifies γ with µ_p (with C=1 in this example), one of these formulas must be wrong. This is not merely a local typo: the minus sign appears already in the displayed limit expression for µ_p and propagates through the p-adic Gamma manipulations. The authors should correct either the theorem statement or the proof, and verify which sign is consistent with the definition (9) and with the p=3 calculation.
  3. [Section 4, p=3 calculation] The congruence -g2/20 ≡ -g2 (mod 3) is arithmetically false: since 20 ≡ 2 (mod 3), one has 1/20 ≡ -1 (mod 3), hence -g2/20 ≡ g2 (mod 3), not -g2. Consequently the displayed derivation of (11) for p=3 is incorrect. In the N=32 example with g2=-16, the computation gives µ_3 ≡ 2 (mod 3) whereas (11) would require µ_3 ≡ -g2 ≡ 1 (mod 3). The non-vanishing conclusion µ_3 ≠ 0 still follows from g2^3 ≡ Δ ≠ 0 (mod 3), so the overall theorem may survive, but (11) as stated does not hold for p=3 in this example and the p=3 case needs a corrected treatment, possibly by changing the sign in (11) or by handling p=3 separately without invoking the Kummer congruence used for p>3.
minor comments (3)
  1. [Abstract and title] The text contains several spacing artifacts in the title and abstract (e.g., "NON-V ANISHING", "CER T AIN") that should be cleaned up in the final version.
  2. [Section 4, paragraph after (11)] The phrase "µ_p is congruent modulo p to p times the coefficient of u^p" is potentially confusing. Since the coefficient of u^p in ζ(Λ,l_t(u)) is -2G_{p+1}/p!, the intended statement is that p times this coefficient is congruent to µ_p modulo p; the wording should be made unambiguous.
  3. [Remark 1] The congruence condition m ≡ (M-1)/2 (mod 2) is not explained and appears to be a provisional guess; it would help to state explicitly that this is a heuristic remark and not a proved formula.

Circularity Check

0 steps flagged · score 2.0 of 10

No circular derivation: the non-vanishing result rests on an independent Eisenstein-series congruence and on classical modular-form facts; only minor reliance on the author's earlier technical lemmas.

full rationale

The central claim is not forced by construction. Existence of beta and gamma is imported from [13, Prop 5], which is an existence statement and does not assert gamma != 0; the new content is to prove gamma != 0. The proof reduces Theorem 3 to (11), mu_p ≡ -E_{p+1}/12 mod p, and (12), E_{p+1} not ≡ 0 mod p at supersingular primes. Congruence (11) is obtained by extracting the coefficient of u^p in zeta(Lambda, l_t(u)) and using Kummer congruences; congruence (12) is proved from the standard fact that the reductions of E_{p-1} and E_{p+1} are relatively prime in the ring of modular forms mod p (Lang, Thm X.7.3(i)), so E_{p+1} is a unit exactly where the Hasse invariant E_{p-1} vanishes. Neither step fits a parameter to the desired conclusion, and the non-vanishing is an externally checkable congruence modulo p. The author's previous work [13] supplies existence of beta,gamma and [14, Cor. 1(a)] supplies invariance of lambda_p,mu_p under strict FGL isomorphisms; these are parameter-free lemmas that do not assume the non-vanishing, so they are self-citations but not circular. A separate correctness gap is the unproved assertion in Section 4 that E_g is strictly isomorphic over Z_p to the fixed p-typical logarithm l_t(u) = Σ(-1)^n u^{p^{2n}}/p^n; Hazewinkel's theorem gives existence of some p-typical FGL, not strict isomorphism to this particular one, and over Z_p height-2 p-typical FGLs are not all strictly isomorphic. This is a mathematical gap in the written proof, not a circularity; the coefficient-of-u^p calculation may be recoverable by a direct height-2 argument. Overall, no fitted-input or definitional circularity is present, so the score is 2 only for the moderate reliance on the author's earlier technical results.

Assumptions & free parameters 0 free parameters · 7 assumptions · 0 invented entities

No new entities are postulated. The central claim rests on several prior theorems, two of which are self-citations ([13], [14]); these provide the existence and the FGL-invariance used to identify constants, but the non-vanishing is not assumed from them. Free parameters: none in the final statements; α, β, λp, µp are determined rather than fitted. The main external benchmarks are the Eisenstein series E_{p+1}.

assumptions (7)
  • domain assumption Existence of a harmonic Maass form f good for g and of α ∈ C such that Fα has rational coefficients.
    Invoked in Section 1 as [7, Proposition 5.1] and [12, Theorem 1.1].
  • domain assumption [13, Proposition 5] gives unique β, γ ∈ Qp such that ord_p(Fα,β,γ) > -∞.
    Used to define γ and in the proof of Proposition 1; the present paper provides no independent proof.
  • standard math Honda's theorem: the formal group of an elliptic curve is strictly isomorphic over Z_p to a Honda formal group of matching height.
    Used in Section 4 to replace the FGL of E with a p-typical FGL and to identify Eg with the FGL logarithm.
  • domain assumption [14, Corollary 1(a)] invariance of λp, µp under strict FGL isomorphism.
    Self-citation; needed to identify the computed constants with the original γ.
  • standard math Dieudonné module D(G) is free of rank 2 with basis ℓ and (1/p)ℓ(t^p) [22, Theorem 5.3.3].
    Used in Section 4 to guarantee λp, µp exist in Z_p.
  • standard math Lang's theorems X.4.2 and X.7.3: E_{p-1} and E_{p+1} are weighted polynomials in E4,E6 that are relatively prime modulo p.
    Core input for the non-vanishing of E_{p+1} at supersingular reductions.
  • standard math Mordell's congruence ((p-1)/2)! ≡ (-1)^{(1+h(-p))/2} (mod p) for p ≡ 3 mod 4, p > 3.
    Used in Theorem 2 to evaluate Γ_p(1/2).

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Pith. "Pith review of Cusp forms as $p$-adic limits circumventing $p$-adic version of the Legendre period relation." pith.science (2026). https://pith.science/paper/WO52OUCL

@misc{pith2026250607107,
  author       = {Pith},
  title        = {Pith review of: Cusp forms as $p$-adic limits circumventing $p$-adic version of the Legendre period relation},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/WO52OUCL}},
  note         = {Machine review of arXiv:2506.07107}
}
abstract

Several authors have recently proved results which express a cusp form as a $p$-adic limit of weakly holomorphic modular forms under repeated application of Atkin's $U$-operator. Initially, these results had a deficiency: one could not rule out the possibility when a certain quantity vanishes and the final result fails to be true. Later on, Ahlgren and Samart \cite{AS} found a method to prove that no exceptions happen in the specific case considered by El-Guindy and Ono, Hanson and Jameson, and (independently) Dicks. generalized this method to finitely many other cases. In this paper, we present a different approach which allows us to prove a similar non-vanishing result for an infinite family of similar cases. Our approach also allows us to return back to the original example considered by El-Guindy and Ono, where we calculate the (manifestly non-zero) quantity explicitly in terms of Morita's $p$-adic $\Gamma$-function.

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Works this paper leans on

34 extracted references · 34 canonical work pages

  1. [1]

    Ahlgren, Scott; Samart, Detchat, A note on cusp forms as p-adic limits. J. Number Theory 168 (2016), 360373

  2. [2]

    From C to Cp

    Andr´ e, Yves, Period mappings and differential equations. From C to Cp. Tˆ ohoku - Hokkaidˆ o lectures in arithmetic geometry. With appendices by F. Kato and N. Tsuzuki. MSJ Memoirs, 12. Mathematical Society of Japan, Tokyo, 2003

  3. [3]

    Bannai, Kenichi; Kobayashi, Shinichi; Yasuda, Seidai, The radius of convergence of the p-adic sigma function. Math. Z. 286 (2017), no. 1-2, 751-781

  4. [4]

    Birch, Bryan; Kuyk, Willem (editors) Numerical tables on elliptic curves in Modular functions of one variable. IV. Proceedings of the International Summer School on Modular Functions of One Variable and Arithmetical Applications, RUCA, University of Antwerp, Antwerp, July 17–August 3, 1972, Lecture Notes in Mathematics, Vol

  5. [5]

    American Mathematical Society Colloquium Publications, 64

    Bringmann, Kathrin; Folsom, Amanda; Ono, Ken; Rolen, Larry, Harmonic Maass forms and mock modular forms: theory and applications. American Mathematical Society Colloquium Publications, 64. American Mathematical Society, Providence, RI, 2017

  6. [6]

    Bringmann, Kathrin; Guerzhoy, Pavel; Kane, Ben, Mock modular forms as p-adic modular forms. Trans. Amer. Math. Soc. 364 (2012), no. 5, 2393-2410

  7. [7]

    Bruinier, Jan H.; Ono, Ken; Rhoades, Robert C., Differential operators for harmonic weak Maass forms and the vanishing of Hecke eigenvalues. Math. Ann. 342 (2008), no. 3, 673-693

  8. [8]

    Ramanujan J

    Dicks, Robert; Weight 2 CM newforms as p-adic limits. Ramanujan J. 58 (2022), no. 4, 1321-1332

Show all 34 references
  1. [9]

    Elkies, Noam D., The existence of infinitely many supersingular primes for every elliptic curve over Q. Invent. Math. 89 (1987), no. 3, 561-567

  2. [10]

    Acta Arith

    El-Guindy, Ahmad; Ono, Ken, Gauss’s 2F1 hypergeometric function and the congru- ent number elliptic curve. Acta Arith. 144 (2010), no. 3, 231-239

  3. [11]

    Number Theory 11 (1979), no

    Gross, Benedict H., On an identity of Chowla and Selberg, J. Number Theory 11 (1979), no. 3, S. Chowla Anniversary Issue, 344-348

  4. [12]

    Guerzhoy, Pavel; Kent, Zachary A.; Ono, Ken, p-adic coupling of mock modular forms and shadows. Proc. Natl. Acad. Sci. USA 107 (2010), no. 14, 6169-6174

  5. [13]

    Guerzhoy, Pavel, On Zagier’s adele. Res. Math. Sci. 1 (2014), Art. 7, 19 pp

  6. [14]

    Guerzhoy, P., On the p-adic values of the weight two Eisenstein series for supersingular primes, preprint, arXiv:2403.02592 [math.NT]

  7. [15]

    Hanson, Michael; Jameson, Marie, Cusp forms as p-adic limits. J. Number Theory 234 (2022), 349-362

  8. [16]

    Corrected reprint of the 1978 original

    Hazewinkel, Michiel, Formal groups and applications. Corrected reprint of the 1978 original. AMS Chelsea Publishing, Providence, RI, 2012

  9. [17]

    Hill, Walter L., Formal groups and zeta-functions of elliptic curves. Invent. Math. 12 (1971), 321-336

  10. [18]

    Honda, Taira, Formal groups and zeta-functions, Osaka J. Math. 5 1968 199-213

  11. [19]

    Springer- Verlag, New York, 2004

    Husem¨ oller, Dale, Elliptic curves, Second edition, With appendices by Otto Forster, Ruth Lawrence and Stefan Theisen, Graduate Texts in Mathematics, 111. Springer- Verlag, New York, 2004

  12. [20]

    Computational perspectives on number theory (Chicago, IL, 1995), 97-126, AMS/IP Stud

    Kaneko, M.; Zagier, D., Supersingular j-invariants, hypergeometric series, and Atkin’s orthogonal polynomials. Computational perspectives on number theory (Chicago, IL, 1995), 97-126, AMS/IP Stud. Adv. Math., 7, Amer. Math. Soc., Providence, RI, 1998

  13. [21]

    Katz, Nicholas M., p-adic interpolation of real analytic Eisenstein series, Ann. of Math. (2) 104 (1976), no. 3, 459-571 19

  14. [22]

    Automorphic forms, representation theory and arithmetic (Bombay, 1979), pp

    Katz, Nicholas M., Crystalline cohomology, Dieudonn´ e modules, and Jacobi sums. Automorphic forms, representation theory and arithmetic (Bombay, 1979), pp. 165- 246, Tata Inst. Fund. Res. Studies in Math., 10, Tata Inst. Fundamental Res., Bom- bay, 1981

  15. [23]

    With appendixes by D

    Lang, S., Introduction to modular forms. With appendixes by D. Zagier and Wal- ter Feit. Corrected reprint of the 1976 original. Grundlehren der Mathematischen Wissenschaften, 222. Springer-Verlag, Berlin, 1995

  16. [24]

    J., The congruence (( p − 1)/2)! ≡ ±1 (mod p), Amer

    Mordell, L. J., The congruence (( p − 1)/2)! ≡ ±1 (mod p), Amer. Math. Monthly 68 (1961), 145-146

  17. [25]

    Ogus, A., A p-adic analogue of the Chowla - Selberg formula, p-adic analysis (Trento,1989), Lecture Notes in Math., 1454, Springer, Berlin, 1990

  18. [26]

    Springer-Verlag, New York, 2000

    Robert, Alain M., A course in p-adic analysis, Graduate Texts in Mathematics, 198. Springer-Verlag, New York, 2000

  19. [27]

    Corrected reprint of the 1986 original

    Silverman, Joseph H., The arithmetic of elliptic curves. Corrected reprint of the 1986 original. Graduate Texts in Mathematics, 106. Springer-Verlag, New York, 1992

  20. [28]

    Ramanujan J

    Tajima, Ryota, The p-adic constant for mock modular forms associated to CM forms. Ramanujan J. 63 (2024), no. 4, 917-929

  21. [29]

    Waldschmidt, Michel, Transcendence of periods: the state of the art, Pure Appl. Math. Q. 2 (2006), no. 2, Special Issue: In honor of John H. Coates. Part 2, 435-463

  22. [30]

    Classics in Mathematics

    Weil, Andr´ e, Elliptic functions according to Eisenstein and Kronecker, Reprint of the 1976 original. Classics in Mathematics. Springer-Verlag, Berlin, 1999

  23. [31]

    Yasuda, Seidai, Explicit t-expansions for the elliptic curve y2 = 4(x3 + Ax + B). Proc. Japan Acad. Ser. A Math. Sci. 89 (2013), no. 9, 123-127

  24. [32]

    Zagier, D., Modular parametrizations of elliptic curves, Canad. Math. Bull. 28 (1985), no. 3, 372-384

  25. [33]

    Bordeaux, 2022, http://pari.math.u-bordeaux.fr/ Department of Mathematics, University of Hawaii, 2565 McCarthy Mall, Honolulu, HI, 96822-2273 Email address : pavel@math.hawaii.edu

    The PARI Group, PARI/GP version 2.13.4, Univ. Bordeaux, 2022, http://pari.math.u-bordeaux.fr/ Department of Mathematics, University of Hawaii, 2565 McCarthy Mall, Honolulu, HI, 96822-2273 Email address : pavel@math.hawaii.edu

  26. [476]

    Springer-Verlag, Berlin-New York, 1975

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