Article
Kyungpook Mathematical Journal 2021; 61(3): 455-459
Published online September 30, 2021
Copyright © Kyungpook Mathematical Journal.
Oh's 8-Universality Criterion is Unique
Scott Duke Kominers
Harvard Business School, Department of Economics, and Center of Mathematical Sciences and Applications, Harvard University, Rock Center 219, Soldiers Field, Boston, MA 02163, USA
e-mail : kominers@fas.harvard.edu
Received: June 8, 2020; Revised: August 30, 2020; Accepted: November 23, 2020
Abstract
We partially characterize criteria for the
Keywords: n-universal lattice, 8-universal lattice, universality criteria, quadratic form, additively indecomposable.
1. Introduction
A degree-two homogeneous polynomial in
A rank-
In 1993, Conway and Schneeberger announced their celebrated
is universal (see [1, 3]). Kim, Kim, and Oh [6] presented an analogous criterion for 2-universality, showing that a positive-definite integer-matrix lattice is 2-universal if and only if it represents the set of forms
Oh [11] gave a similar criterion for 8-universality, which we state in Theorem 4.1 of Section 4.
A set
The set
Kim, Kim, and Oh [7] have proven that
Since we first circulated this paper, there has been renewed attention in characterizing criterion sets: Elkies, Kane, and the author [5] identified several families of lattices for which there exist multiple universality criteria of different sizes, including one based on the
2. Notation and Terminology
We use the lattice-theoretic language of quadratic form theory. A complete introduction to this approach may be found in [12]. In addition, we use the lattice notation of [4], under which
For a
For a sublattice ℓ of
with
3. Partial Characterization of n-Criterion Sets
In this section, we prove two results that partially characterize the contents of arbitrary
Proposition 3.1.
We may therefore write
where
represents all of
Proposition 3.2. it Let
which of course represents all of
If
Thus, we have found a lattice that represents all of
Remark 3.3. It is clear that direct analogues of Propositions 3.1 and 3.2 hold in the more general setting of
4. Uniqueness of The 8-Criterion Set
Oh [11] obtained the following
The set
Corollary 4.2, when combined with Theorem 4.1, shows that
Acknowledgements
The author is grateful to Pablo Azar, Noam D. Elkies, Andrea J. Hawksley, Sonia Jaffe, Paul M. Kominers, and especially Ravi Jagadeesan for helpful comments and suggestions, and particularly thanks an anonymous referee for pointing out a problem with the original form of Proposition 3.2.
References
- M. Bhargava, On the Conway-Schneeberger fifteen theorem, Quadratic forms and their applications (Dublin, 1999), 27-37, Contemp. Math. 272, Amer. Math. Soc., Providence, RI, 2000.
- W. K. Chan and B.-K. Oh, On the exceptional sets of integral quadratic forms, Int. Math. Res. Notices, https://doi.org/10.1093/imrn/rnaa382.
- J. H. Conway, Universal quadratic forms and the fifteen theorem, Quadratic forms and their applications (Dublin, 1999), 2326, Contemp. Math. 272, Amer. Math. Soc., Providence, RI, 2000.
- J. H. Conway and N. J. A. Sloane, Low-dimensional lattices I. Quadratic forms of small determinant, Proc. Roy. Soc. London Ser. A, 418(1854)(1988), 17-41.
- N. D. Elkies, D. M. Kane and S. D. Kominers, Minimal S-universality criteria may vary in size, J. Théor. Nombres Bordeaux, 25(3)(2013), 557-563.
- B. M. Kim and M.-H. Kim and B.-K. Oh, 2-universal positive definite integral quinary quadratic forms, Integral quadratic forms and lattices (Seoul, 1998), 5162, Contemp. Math. 249, Amer. Math. Soc., Providence, RI, 1999.
- B. M. Kim and M.-H. Kim and B.-K. Oh, A finiteness theorem for representability of quadratic forms by forms, J. Reine Angew. Math., 581(2005), 23-30.
- K. Kim and J. Lee and B.-K. Oh, Minimal universality criterion sets on the representations of quadratic forms, (2020), preprint, arXiv:2009.04050.
- S. D. Kominers, Uniqueness of the 2-universality criterion, Note Mat., 28(2)(2008), 203-206.
- J. Lee, Minimal S-universality criterion sets, Seoul National University, Thesis (Ph.D.), 2020.
- B.-K. Oh, Universal Z-lattices of minimal rank, Proc. Amer. Math. Soc., 128(3)(2000), 683-689.
- O. T. O’Meara, Introduction to quadratic forms, Springer-Verlag, New York, 2000.