Each Invertible Sharply d-Transitive Finite Permutation Set with d ≥ 4 is a Group

All known finite sharply 4-transitive permutation sets containing the identity are groups, namely S ₄, S ₅, A ₆ and the Mathieu group of degree 11. We prove that a sharply 4-transitive permutation set on 11 elements containing the identity must necessarily be the Mathieu group of degree 11. The proof uses direct counting arguments. It is based on a combinatorial property of the involutions in the Mathieu group of degree 11 (which is established here) and on the uniqueness of the Minkowski planes of order 9 (which had been established before): the validity of both facts relies on computer calculations. A permutation set is said to be invertible if it contains the identity and if whenever it contains a permutation it also contains its inverse. In the geometric structure arising from an invertible permutation set at least one block-symmetry is an automorphism. The above result has the following consequences. i) A sharply 5-transitive permutation set on 12 elements containing the identity is necessarily the Mathieu group of degree 12. ii) There exists no sharply 6-transitive permutation set on 13 elements. For d 6 there exists no invertible sharply d-transitive permutation set on a finite set with at least d + 3 elements. iii) A finite invertible sharply d-transitive permutation set with d 4 is necessarily a group, that is either a symmetric group, an alternating group, the Mathieu group of degree 11 or the Mathieu group of degree 12.     

Extension of Multiply Transitive Permutation Sets

Let G be a k-transitive permutation set on E and let E* = E∪{∞},∞ ? E; if G* is a (k: + 1)-transitive permutation set on E*, G* is said to be an extension of G whenever G _∝ ^* =G. In this work we deal with the problem of extending (sharply) k- transitive permutation sets into (sharply) (k + 1)-transitive permutation sets. In particular we give sufficient conditions for the extension of such sets; these conditions can be reduced to a unique one (which is a necessary condition too) whenever the considered set is a group. Furthermore we establish necessary and sufficient conditions for a sharply k- transitive permutation set (k ≥ 3) to be a group. Math. Subj. Class.: 20B20 Multiply finite transitive permutation groups 20B22 Multiply infinite transitive permutation groups     

Over the non-existence of sharply 3-transitive permutation sets containing sharply 2-transitive permutation subsets

The following results are proved: Let E be a finite set, ¦E¦>4, and let G be a sharply 3-transitive permutation set on E. Then G contains no subset which is a sharply 2-transitive permutation set on E (Theorem 1). In the case when G is a sharply 3-transitive permutation group which is also planar, the finiteness condition on E can be dropped (Theorem 2).Dedicated to G. Zappa on his 70th birthdayResearch done within the activity of GNSAGA of CNR, supported by the 40% grants of MPI.     

On the sharply 1-transitive subsets of PGL(2,pm)

If p is an odd prime and R is a sharply 1-transitive subset of PGL(2,p^m) which contains the identity but is not a group, then the subgroup generated by R is either PSL(2,p^m) or PGL(2,p^m).work done within the activity of G.N.S.A.G.A. and supported by the Italian Ministry of Public EducationDedicated to Professor Helmut Karzel on his 60^th birthday     

Über die Normalteiler scharf zweifach und scharf dreifach transitiver Permutationsgruppen

A sharply 2-transitive (3-transitive) groupT can be described by means of a neardomainF (a KT-field(F,)). We show, thatT has a least nontrivial normal subgroupA (S(F,)), ifF is a nearfield or if CharF 2. In this case the nontrivial normal subgroups ofT correspond bijectively with all normal subgroupsF ^* (the multiplicative group ofF) containing a setD (D(Q)). IfF is a nearfield or ifF has a suitable central element, then the group S(F,) is simple.

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Herrn Prof. Dr. Dr. h. c. Helmut Karzel zum 70. Geburtstag gewidmet     

Primitive permutation groups with a regular subgroup

This paper starts the classification of the primitive permutation groups (G,Ω) such that G contains a regular subgroup X. We determine all the triples (G,Ω,X) with soc(G) an alternating, or a sporadic or an exceptional group of Lie type. Further, we construct all the examples (G,Ω,X) with G a classical group which are known to us. Our particular interest is in the 8-dimensional orthogonal groups of Witt index 4. We determine all the triples (G,Ω,X) with . In order to obtain all these triples, we also study the almost simple groups G with GPΩ_2n+1(q). The case GU_n(q) is started in this paper and finished in [B. Baumeister, Primitive permutation groups of unitary type with a regular subgroup, Bull. Belg. Math. Soc. 112 (5) (2006) 657–673]. A group X is called a Burnside-group (or short a B-group) if each primitive permutation group which contains a regular subgroup isomorphic to X is necessarily 2-transitive. In the end of the paper we discuss B-groups.     

On minimal p-degrees in 2-transitive permutation groups

Suppose G is a transitive permutation group on a finite set W\mit\Omega of n points and let p be a prime divisor of |G||G|. The smallest number of points moved by a non-identity p-element is called the minimal p-degree of G and is denoted m_p (G). ¶ In the article the minimal p-degrees of various 2-transitive permutation groups are calculated. Using the classification of finite 2-transitive permutation groups these results yield the main theorem, that m_p(G) 3 [(p-1)/(p+1)] ·|W|m_{p}(G) \geq {{p-1} \over {p+1}} \cdot |\mit\Omega | holds, if Alt(W) \nleqq G {\rm Alt}(\mit\Omega ) \nleqq G .¶Also all groups G (and prime divisors p of |G||G|) for which m_p(G) ￡ [(p-1)/(p)] ·|W|m_{p}(G)\le {{p-1}\over{p}} \cdot |\mit\Omega | are identified.     

Desarguesian finite generalized quadrangles are classical or dual classical

Let S = (P, B, I) be a finite generalized quadrangle of order (s, t), s > 1, t > 1. Given a flag (p, L) of S, a (p, L)-collineation is a collineation of S which fixes each point on L and each line through p. For any line N incident with p, N L, and any point u incident with L, u p, the group G(p, L) of all (p, L)-collineations acts semiregularly on the lines M concurrent with N, p not incident with M, and on the points w collinear with u, w not incident with L. If the group G(p, L) is transitive on the lines M, or equivalently, on the points w, then we say that S is (p, L)-transitive. We prove that the finite generalized quadrangle S is (p, L)-transitive for all flags (p, L) if and only if S is classical or dual classical. Further, for any flag (p, L), we introduce the notion of (p, L)-desarguesian generalized quadrangle, a purely geometrical concept, and we prove that the finite generalized quadrangle S is (p, L)-desarguesian if and only if it is (p, L)-transitive.Research Associate of the National Fund for Scientific Research (Belgium).     

Cyclic Ostrom Spreads

We call a transitive permutation group G stable if every non-trivial orbit B, of a point stabilizerG _O , is such that some element of G-G _O leaves invariant B {O}. We characterize all finite affine planes of order n that admit a collineation group G that acts, on the points of , as a stable 3/2-transitive permutation group of rank n+2 . The planes obtained are precisely what we have called cyclic Ostrom planes; these are translation planes whose associated spreads are obtained from the Desarguesian spread , of order n=p^r , by replacing a partial subspread of by another consisting of GF(p) subspaces that are unions of kern orbits. All André spreads, as well as many other spreads, are examples of cyclic Ostrom spreads.     

Tetravalent s-Transitive Graphs of Order 4p 2

Let s be a positive integer. A graph is s -transitive if its automorphism group is transitive on s-arcs but not on (s?+?1)-arcs. Let p be a prime. Zhou (Discrete Math 309:6081?C6086, 2009) classified tetravalent s-transitive graphs of order 4p. In this article a complete classification of tetravalent s-transitive graphs of order 4p ² is given.     

Endomorphisms of superelliptic jacobians

Let K be a field of characteristic zero, n ≥ 5 an integer, f(x) an irreducible polynomial over K of degree n, whose Galois group contains a doubly transitive simple non-abelian group. Let p be an odd prime, the ring of integers in the pth cyclotomic field, C _{f, p} : y ^p  =  f(x) the corresponding superelliptic curve and J(C _{f, p} ) its jacobian. Assuming that either n  =  p + 1 or p does not divide n(n  −  1), we prove that the ring of all endomorphisms of J(C _{f, p} ) coincides with . The same is true if n  =  4, the Galois group of f(x) is the full symmetric group S ₄ and K contains a primitive pth root of unity. An erratum to this article can be found at     

On projective planes of type (4, m)

If a group G acts on a finite projective plane to make it a plane of type (4, m) and if G/K is the related 2-transitive representation of G then either G/K has a normal regular subgroup or PSL(2, q)G/KPL(2, q) for some prime power q.     

On the <Emphasis Type="Italic">L</Emphasis><Superscript><Emphasis Type="Italic">p</Emphasis></Superscript>-conjecture for locally compact groups

Let G be a locally compact group. For 1 < p < ∞, it is well-known that f * g exists and belongs to L^p(G) for all f, g L^p (G) if and only if G is compact. Here, for 2 < p < ∞, we show that f * g exists for all f, g L^p(G) if and only if G is compact. We also show that this result does not remain true for 1 < p ≤ 2. Received: 23 April 2006     

The algebraic radical of a normed ideal inL 1(G)

LetA be a proper normed ideal (in the sense ofCigler) insideL ¹ (G), whereG is a non-discrete LCA group. This is proved: For each integern1 there existsfL ¹ (G) such thatf, f ² ,..., f ^nA whilef ⁿ⁺¹ A.     

Proof of Oppenheim's area inequalities for triangles and quadrilaterals

Leta ₁,b ₁,c ₁,A ₁ anda ₂,b ₂,c ₂,A ₂ be the sides and areas of two triangles. Ifa=(a ₁ ^p +a ₂ ^p )^1/p ,b=(b ₁ ^p +b ₂ ^p )^1/p ,c=(c ₁ ^p +c ₂ ^p )^1/p , and 1p4, thena, b, c are the sides of a triangle and its area satisfiesA ^p/2A ₁ ^p/2 +A ₂ ^p/2 . If obtuse triangles are excluded,p>4 is allowed. For convex cyclic quadrilaterals, a similar inequality holds. Also, leta, b, c, A be the sides and area of an acute or right triangle. Iff(x) satisfies certain conditions,f(a),f(b),f(c) are the sides of a triangle having areaA _f, which satisfies (4A _f/3)^1/2f((4A/3)^1/2).     

Formulas for the Inverses of Toeplitz Matrices with Polynomially Singular Symbols

We consider large finite Toeplitz matrices with symbols of the form (1– cos )^p f() where p is a natural number and f is a sufficiently smooth positive function. By employing techniques based on the use of predictor polynomials, we derive exact and asymptotic formulas for the entries of the inverses of these matrices. We show in particular that asymptotically the inverse matrix mimics the Green kernel of a boundary value problem for the differential operator Submitted: June 20, 2003     

Regularized spectral distributions

For C a bounded, injective operator with dense image, we define a C-regularized spectral distribution. This produces a functional calculus, f f(B), from C() into the space of closed densely defined operators, such that f(B)C is bounded when f has compact support. As an analogue of Stone's theorem, we characterize certain regularized spectral distributions as corresponding to generators of polynomially bounded C-regularized groups. We represent the regularized spectral distribution in terms of the regularized group and in terms of the C-resolvent. Applications include the Schrödinger equation with potential, and symmetric hyperbolic systems, all on L^p(ⁿ) (1p<), C _o(ⁿ), BUC(ⁿ), or any space of functions where translation is a bounded strongly continuous group.     

A Coding Theory Bound and Zero-Sum Square Matrices

For a code C=C(n,M) the level k code of C, denoted C _k , is the set of all vectors resulting from a linear combination of precisely k distinct codewords of C. We prove that if k is any positive integer divisible by 8, and n=k, M=k2k then there is a codeword in C _k whose weight is either 0 or at most . In particular, if <(4–2)²/48 then there is a codeword in C _k whose weight is n/2–(n). The method used to prove this result enables us to prove the following: Let k be an integer divisible by p, and let f(k,p) denote the minimum integer guaranteeing that in any square matrix over Z _p , of order f(k,p), there is a square submatrix of order k such that the sum of all the elements in each row and column is 0. We prove that lim inf f(k,2)/k<3.836. For general p we obtain, using a different approach, that f(k,p)p( ^{k / ln k )(1+ o} _k ⁽¹⁾⁾.     

Benz planes of Dembowski type and groups of tangential projectivities

Using the tangential relation we introduce in Benz planes M of Dembowski type, which generalize the Benz planes over algebras of characteristic 2, the group ?? of tangential perspectivities. We prove that these groups have the same behaviour as the classical groups of projectivities if any tangential perspectivity is induced by an automorphism of M. As permutation groups of a circle onto itself the groups ?? essentially differs from the classical groups of projectivities. If M is a Laguerre plane of Dembowski type, then ?? is always sharply 3-transitive. For Minkowski planes of Dembowski type ?? is at least 2-transitive. If M is a finite Benz plane of order 2 ^s , then ?? is isomorphic to the group PGL ₂(2 ^s ) in its sharply 3-transitive representation.     

Taking pth Roots Modulo Polynomials over Finite Fields

In this contribution we show how to find y(x) in the polynomial equation y(x) ^p t(x) mod f(x), where t(x), y(x) and f(x) are polynomials over the field GF(p ^m). The solution of such equations are thought for in many cases, e.g., for p = 2 it is a step in the so-called Patterson Algorithm for decoding binary Goppa codes.