Split BN-pairs of rank 2: the octagons

Let G be a group with an irreducible spherical BN-pair of rank 2 where B contains a normal nilpotent subgroup U with B=U(B∩N). Then G is essentially a group of Lie type. This completes the classification of split BN-pairs of rank 2, generalizing the corresponding result for finite groups due to Fong and Seitz.     

Constructions of rank five geometries for the Mathieu group M 22

We construct nine rank five incidence geometries that are firm and residually connected and on which the Mathieu group M²² acts flag-transitively. The constructions use mainly objects arising from the Steiner systemS(3, 6, 22). One of these geometries was constructed by Meixner and Pasini in [10]. Three of them are obtained from the geometry of Meixner and Pasini using doubling (see [8] or [12]) or similar constructions. The remaining five are new and four of them have a star diagram. These latter four geometries are constructed using special partitions of the 22 points of the Steiner system S(3, 6, 22).     

A characterization of 3-local geometry of M(24)

The largest Fischer 3-transposition group M(24) acts flag-transitively on a 3-local incidence geometry (M(24)) which is a c-extension of the dual polar space associated with the group O ₇(3). The action of the simple commutator subgroup M(24) is still flag-transitive. We show that (M(24)) is characterized by its diagram under the flag-transitivity assumption. The result implies in particular that (M(24)) is simply connected. The geometry (M(24)) appears as a subgeometry in the Buekenhout-Fischer 3-local geometry (F ₁) of the Monster group. The simple connectedness of (M(24)) has played a crucial role in the characterization of (F ₁), which has been achieved recently. When determining the possible structure of the parabolic subgroups we have used an unpublished pushing-up result by U. Meierfrankenfeld.Dedicated to Professor B. Fischer on the occasion of his sixtieth birthday     

A geometry for groups of <Emphasis Type="Italic">J</Emphasis><Subscript>3</Subscript>-type

The proof of the existence and of the uniqueness of groups of J₃-type by G. Higman and J. McKay is based on the fact that a group of J₃-type is a faithful completion of an amalgam of J₃-type, see [11]. In this paper here, we provide a direct reference for that fact. The proofs in this paper are elementary and we do not use any character theory. Received: 1 December 2005     

Direct sum decomposition of geometries based on maximal subgroups

In 1961 J. Tits described a way to define a geometry from a group and a collection of subgroups. Such incidence geometries are now studied by the team of F. Buekenhout in Brussels. Here we present theorems about decomposition of PRI geometries into direct sums and we find the full direct sum decomposition of PRI geometries on solvable groups.     

On homomorphisms between generalized polygons

We consider homomorphisms between abstract, topological, and smooth generalized polygons. It is shown that a continuous homomorphism is either injective or locally constant. A continuous homomorphism between smooth generalized polygons is always a smooth embedding. We apply this result to isoparametric submanifolds.Dedicated to Prof. Dr. H. R. Salzmann on the occasion of his 65th anniversary     

Nets and generalized quadrangles

There is a new method of constructing generalized quadrangles (GQs) given by S. Löwe, which is based on covering of nets; all GQs with a regular point can be represented in this way. Here we give a method of constructing GQs with a regular point using the so-called content functions on nets. In the last part of the paper we lay the foundations for a research project aiming to use the more general notion of content to classify GQs and maybe to construct new ones.Both authors acknowledge the financial support by CRUI and DAAD in the frame of Programma Vigoni, which made this work possible.     

Finite distance-transitive generalized polygons

Using the classification of the finite simple groups, we classify all finite generalized polygons having an automorphism group acting distance-transitively on the set of points. This proves an old conjecture of J. Tits saying that every group with an irreducible rank 2 BN-pair arises from a group of Lie type.Research Associate of the National Fund for Scientific Research (Belgium).     

Sharp homogeneity in some generalized polygons

We show that, if a collineation group G of a generalized (2n + 1)-gon $\Gamma$ has the property that every symmetry of any apartment extends uniquely to a collineation in G, then $\Gamma$ is the unique projective plane with 3 points per line (the Fano plane) and G is its full collineation group. A similar result holds if one substitutes apartment with path of length 2k 2n + 2.Received: 19 June 2002     

Algebraic radicals and incidence algebras

In this note we prove the uniqueness of U in a group G with a spherical split-BN-pair of rank ,i.e., if G has such a BN-pair with a nilpotent normal subgroup of B, and , then and is a normal subgroup of G. Here is the corresponding group of Lie-type and the subgroup of generated by all root-subgroups corresponding to positive roots. Received: 19 May 2003     

Conic blocking sets in Desarguesian projective planes

Define a conic blocking set to be a set of lines in a Desarguesian projective plane such that all conics meet these lines. Conic blocking sets can be used in determining if a collection of planes in projective three-space forms a flock of a quadratic cone. We discuss trivial conic blocking sets and conic blocking sets in planes of small order. We provide a construction for conic blocking sets in planes of non-prime order, and we make additional comments about the structure of these conic blocking sets in certain planes of even order.     

Generalized polygons with highly transitive collineation groups

It will be proved that the compact connected topological generalized quadrangles which admit a collineation group that acts transitively on ordered pentagons are precisely the real or complex orthogonal quadrangles, up to duality.Dedicated to Prof. H. Salzmann on the occasion of his 65th birthday     

Translation Generalized Quadrangles In Even Characteristic

In this paper, we first introduce new objects called “translation generalized ovals” and “translation generalized ovoids”, and make a thorough study of these objects. We then obtain numerous new characterizations of the of Tits and the classical generalized quadrangle in even characteristic, including the complete classification of 2-transitive generalized ovals for the even case. Next, we prove a new strong characterization theorem for the of Tits. As a corollary, we obtain a purely geometric proof of a theorem of Johnson on semifield flocks. * The second author is a Postdoctoral Fellow of the Fund for Scientific Research—Flanders (Belgium).     

Spherical Harmonic Analysis on Buildings of Type à n

 To any locally finite thick building of type there is naturally associated a commutative algebra of operators. When is constructed from a local field F with local ring , and , then is isomorphic to the convolution algebra of compactly supported bi-K-invariant functions on PGL(n+1,F). We give a proof, valid for any , that the multiplicative functionals on may all be expressed in terms of Hall–Littlewood polynomials. Regarding as a subalgebra of the C ^*-algebra of bounded operators on the space of square summable functions on the vertex set of , we find the spectrum of the C ^*-algebra , the closure of . This generalizes results obtained in [3] when n = 1 and in [5] when n = 2. (Received 26 June 2000; in revised form 21 February 2001)     

Tubes of even order and flat π.C 2 geometries

Atube of even orderq=2 ^d is a setT={L, } ofq+3 pairwise skew lines in PG(3,q) such that every plane onL meets the lines of in a hyperoval. Thequadric tube is obtained as follows. Take a hyperbolic quadricQ=Q ₃ ⁺ (q) in PG(3,q); letL be an exterior line, and let consist of the polar line ofL together with a regulus onQ.In this paper we show the existence of tubes of even order other than the quadric one, and we prove that the subgroup of PL(4,q) fixing a tube {L, } cannot act transitively on . As pointed out by a construction due to Pasini, this implies new results for the existence of flat .C ₂ geometries whoseC ₂-residues are nonclassical generalized quadrangles different from nets. We also give the results of some computations on the existence and uniqueness of tubes in PG(3,q) for smallq. Further, we define tubes for oddq (replacing hyperoval by conic in the definition), and consider briefly a related extremal problem.Dedicated to luigi antonio rosati on the occasion of his 70th birthday     

On inductively minimal geometries that satisfy the intersection property

We prove that, up to isomorphism, for a given positive integer n, there is only one inductively minimal pair (Γ,Sym(n)) of rank n-1 that satisfies the intersection property. Moreover, we show that the diagram of Γ is linear.     

Varieties of finite supersolvable groups with the M. Hall property

The varieties in the title are shown to be precisely the product varieties G_p*Ab(d) for some prime p and some positive integer d dividing p−1. Here G_p denotes the variety of all finite p-groups and Ab(d) the variety of all finite Abelian groups of exponent dividing d. It turns out that these are exactly those varieties H of supersolvable groups for which all finitely generated free pro-H groups are freely indexed in the sense of Lubotzky and van den Dries. Several alternative characterizations of these varieties are presented. Some applications to formal language theory and finite monoid theory are also given. Among these is the determination of all supersolvable solutions H to the equations PH = J*H and J*H = J H which is, to the present date, the most complete solution to a problem raised by Pin. Another consequence of our results is that for each such variety H the monoid variety PH = J*H = J H has decidable membership. The authors gratefully acknowledge the support of NSERC     

THE FISCHER-CLIFFORD MATRICES OF THE GROUP 26: SP 6(2)

Abstract

The smallest Fischer sporadic simple group F₂₂ has 14 maximal subgroups up to conjugacy as listed in [2] and [15]. The group 2⁶: SP ₆(2) is a maximal subgroup of F ₂₂ of index 694980. We use the technique of the Fischer-Clifford matrices to constuct the character table of the group 2⁶: SP ₆(2). The Fischer-Clifford matrices of 2⁶: SP ₆(2) are used, together with the character tables of SP ₆(2) and a maximal subgroup 2⁵:S ₆ SP ₆ (2) of index 63, to construct the character table of 2⁶: SP ₆ (2).