We study how to formalize in the Coq proof assistant the smallest projective space PG(3,2). We then describe formally the spreads and packings of PG(3,2), as well as some of their properties. The formalization is rather straightforward, however as the number of objects at stake increases rapidly, we need to exploit some symmetry arguments as well as smart proof techniques to make proof search and verification faster and thus tractable using the Coq proof assistant. This work can be viewed as a first step towards formalizing projective spaces of higher dimension, e.g. PG(4,2), or larger order, e.g. PG(3,3).
This paper will give both the necessary and sufficient conditions required to find a counter-example to the Goldbach Conjecture by using an algebraic approach where no knowledge of the gaps between prime numbers is needed. To eliminate ambiguity the set of natural numbers, $\mathbb{N}$, will include zero throughout this paper. Also, for any sufficiently large $a \in \mathbb{N}$ the set $\mathcal{P}$ is the set of all primes $p_i \leq a$. It will be shown there exists a counter-example to the Goldbach Conjecture, given by $2a$ where $a \in \mathbb{N}_{> 3}$, if and only if for each prime $p_i \in \mathcal{P}$ there exists some unique $q_i, \alpha_i \in \mathbb{N}$ where $a 3$. However, this leads to contradiction since $2a 4$.A similar method will be employed to give the necessary and sufficient conditions when an even number is not the difference of two primes with one prime being less than that even number. To begin, let $a \in \mathbb{N}_{> 3}$ with the condition that the function $\gamma(a + 1)$ is equal to one if $a + 1$ is prime and zero otherwise. $2a$ is a counter-example if and only if for each prime $p_i \in \mathcal{P}$ there exists some unique $u_i, \beta_i \in \mathbb{N}$ where $2a 3$ to the equation above, leading to the same contradiction as the Goldbach Conjecture since $2a 4$. These proofs will have implications for proving the Polignac Conjecture.
Yiannis Sakellaridis and Akshay Venkathesh have determined, when the group\n$G$ is split and the field $\\F$ is of characteristic zero, the Plancherel\nformula for any spherical space $X$ for $G$ modulo the knowledge of the\ndiscrete spectrum.\n The starting point is the determination of good neighborhoods at infinity of\n$X/J$, where $J$ is a small compact open subgroup of $G$. These neighborhoods\nare related to "boundary degenerations" of $X$. The proof of their existence is\nmade by using wonderful compactifications.\n In this article we will show the existence of such neighborhoods assuming\nthat $\\F$ is of characteristic different from 2 and $X$ is symmetric. In\nparticular, one does not assume that $G$ is split. Our main tools are the\nCartan decomposition of Benoist and Oh, our previous definition of the constant\nterm and asymptotic properties of Eisenstein integrals due to Nathalie Lagier .\n Once the existence of these neighborhoods at infinity of $X$ is established,\nthe analog of the work of Sakellaridis and Venkatesh is straightforward and\nleads to the Plancherel formula for $X$.\n
Let Γ denote the modular group SL(2,Z) and Cn(Γ) the number of congruence subgproups of Γ of index at most n. We prove that lim n→∞ log Cn(Γ) (log n)2/ log log n = 3−2 √ 2 4 . Some extensions of this result for other arithmetic groups are presented as well as a general conjecture. §0. Introduction Let k be an algebraic number field, O its ring of integers, S a finite set of valuations of k (containing all the archimedean ones), and OS = { x ∈ k ∣∣ v(x) ≥ 0, ∀v ∈ S}. Let G be a semisimple, simply connected, connected algebraic group defined over k with a fixed embedding into GLd. Let Γ = G(OS) = G ∩ GLd(OS) be the corresponding S-arithmetic group. We assume that Γ is an infinite group. For every non-zero ideal I of OS let Γ(I) = Ker ( Γ → GLd(OS/I) ) . A subgroup of Γ is called a congruence subgroup if it contains Γ(I) for some I. For n > 0, define Cn(Γ) = # { congruence subgroups of Γ of index at most n } . Theorem 1. There exist two positive real numbers α− and α+ such that for all sufficiently large positive integers n n log n log log nα− ≤ Cn(Γ) ≤ n log n log log nα+ . This theorem is proved in [Lu], although the proof of the lower bound presented there requires the prime number theorem on arithmetic progressions in an interval where its validity depends on the GRH (generalized Riemann hypothesis for arithmetic progressions). The first two authors research is supported in part by the NSF. The third author’s Research is supported in part by OTKA T 034878. All three authors would like to thank Yale University for its hospitality. Typeset by AMS-TEX 1 2 DORIAN GOLDFELD ALEXANDER LUBOTZKY LASZLO PYBER In §2 below, we show that by appealing to a theorem of Linnik [Li1, Li2] on the least prime in an arithmetic progression, the proof can be made unconditional. Following [Lu] we define: α+(Γ) = lim logCn(Γ) λ(n) , α−(Γ) = lim logCn(Γ) λ(n) , where λ(n) = (log n) 2 log log n . It is not difficult to see that α+ and α− are independent of both the choice of the representation of G as a matrix group, as well as independent of the choice of S. Hence α± depend only on G and k. The question whether α+(Γ) = α−(Γ) and the challenge to evaluate them for Γ = SL2(Z) and other groups were presented in [Lu]. It was conjectured by Rademacher that there are only finitely many congruence subgroups of SL2(Z) of genus zero. This counting problem has a long history. Petersson [Pe, 1974] proved that the number of all subgroups of index n and fixed genus goes to infinity exponentially as n → ∞. Dennin [De, 1975] proved that there are only finitely many congruence subgroups of SL2(Z) of given fixed genus and solved Rademacher’s conjecture. It does not seem possible, however, to accurately count all congruence subgroups of index at most n in SL2(Z) by using the theory of Riemann surfaces of fixed genus. Here we prove: Theorem 2. α+(SL2(Z)) = α−(SL2(Z)) = 3−2 √ 2 4 = 0.0428932 . . . We believe that SL2(Z) represents the general case and we expect that α+ = α− for all groups. The proof of the lower bound in Theorem 2 is based on the Bombieri-Vinogradov Theorem [Bo], [Da], [Vi], i.e., the Riemann hypothesis on the average. The upper bound, on the other hand, is proved by first reducing the problem to a counting problem for subgroups of abelian groups and then solving that extremal counting problem. We will, in fact, show a more remarkable result: the answer is independent of O! Theorem 3. Let k be a number field with Galois group g = Gal(k/Q) and with ring of integers O. Let S be a finite set of primes, and OS as above. Assume GRH (generalized Riemann hypothesis) for k and all cyclotomic extensions k(ζ ) with a rational prime and ζ a primitive th root of unity. Then α+(SL2(OS)) = α−(SL2(OS)) = 3 − 2 √ 2 4 . The GRH is needed only for establishing the lower bound. It can be dropped in many cases by appealing to a theorem of Murty and Murty [MM] which generalizes the Bombieri– Vinogradov Theorem cited earlier. COUNTING CONGRUENCE SUBGROUPS 3 Theorem 4. Theorem 3 can be proved unconditionally for k if either (a) g = Gal(k/Q) has an abelian subgroup of index at most 4 (this is true, for example, if k is an abelian extension); (b) d = deg[k : Q] < 42. We conjecture that for every Chevalley group scheme G, the upper and lower limiting constants, α±(G(OS)), depend only on G and not on O. In fact, we have a precise conjecture, for which we need to introduce some additional notation. Let G be a Chevalley group scheme of dimension d = dim(G) and rank = rk(G). Let κ = |Φ+| denote the number of positive roots in the root system of G. Letting R = R(G) = d− 2 = κ , we see that R = +1 2 , (resp. , , −1, 3, 6, 6, 9, 15) if G is of type A (resp. B , C , D , G2, F4, E6, E7, E8). Conjecture. Let k,O, and S be as in Theorem 3, and suppose that G is a simple Chevalley group scheme. Then α+(G(OS)) = α−(G(OS)) = (√ R(R + 1) −R )2 4R2 . The conjecture reflects the belief that “most” subgroups of H = G(Z/mZ) lie between the Borel subgroup B of H and the unipotent radical of B. Our proof covers the case of SL2 and we are quite convinced that this will hold in general. For general G, we do not have such an in depth knowledge of the subgroups of G(Fq) as we do for G = SL2, yet we can still prove: Theorem 5. Let k,O, and S be as in Theorem 3. Let G be a simple Chevalley group scheme of dimension d and rank , and R = R(G) = d− 2 , then: (a) Assuming GRH or the assumptions of Theorem 4; α−(G(OS)) ≥ (√ R(R + 1) −R )2
This thesis is an attempt to generalise to the odd orthogonal group Γ_K, over an Infinite field K not of characteristic two, the work of Schur [S], and more recently Green [G], on the general linear group G_K using the approach of Weyl [W] in characteristic zero. The special feature here is that we treat Γ_K as merely a group of matrices defined by the vanishing of polynomials in its coefficients (the classical view) rather than a group generated by elements derived from an associated Lie algebra, the approach used initially by Chevalley and adopted by most authors in recent times. \n \nAfter generalising Green's [G] Schur algebra for G_K to Γ_K in §0 we prove in §1 Chevalley's famous theorem on the 'Big Cell' in G_K and then, by an easy extension, prove it for the Big Cell in Γ_K. Chevalley's original proof uses representations of Lie algebras, ours requires nothing but a little knowledge of the coordinate ring K_+[G] of all 'polynomial' functions on G_K . We define K[Γ], the coordinate ring of Γ_K, to be the space of all polynomial functions on G_K restricted to Γ_K and in §2 give a generating set of the kernel of the restriction map ψ_K:K_+ [G]→K[Γ]. This generalises Weyl's result in characteristic zero. In §3 we use this result to show that the family, or 'scheme', of rings K[Γ] (K varying over all infinite fields not of characteristic two) is 'defined over Z' ; in fact K[Γ] is naturally isomorphic to K θ Z[Γ_Q], where Z[Γ_Q] is the subring of Q[Γ] spanned by 'monomial' functions. This enables us to formulate a 'modular' representation theory for Γ which connects polynomial representations of Γ_Q with those of Γ_K. \n \nIn §4 we investigate the Schur algebras of Γ_Q following Weyl [W] and in §5 find a complete set of irreducibles for each of them, once again following the lead of Weyl. In §6 we attempt to 'reduce' these modules modulo p to obtain 'Weyl' modules for Γ_K, a task only partially completed.
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Advanced Algebra and Geometry
Finite Group Theory Research
Advanced Differential Equations and Dynamical Systems