Konstruktion topologischer affiner Ebenen mit nichtstetigem Parallelismus durch Knicken von Geraden

We prove the existence of a class of topological affine planes having non-continuous parallelism by using [2, Satz 5.2]. For this, we introduce a new method of constructing affine Salzmann-planes with a monotonically increasing slope (see 2.1) by bending lines on two special curves, which are not necessary lines. Furthermore, the limit inferior of a sequence of topological planes with fixed point space is defined. As application of our new method, we construct a sequence of affine Salzmann-planes such that the limit inferior of this sequence is again an affine Salzmann-plane and fulfils the assumptions of [2, Satz 5.2]. Applying this theorem repeatedly, we get a sequence of non-isomorphic topological affine subplanes with non-continuous parallelism.     

Pasting of R 2-planes

The notion pasting sum (P _i , _i ) of two R ²-planes (or Salzmann planes) (P _i , _i ) is developed. Necessary and sufficient conditions for it to be an R ²-plane again are given. The notion is applied to classify all flat projective planes whose collineation group contains a sub-group with (isomorphism type of , fixed element configuration)=(², x).     

Compact interval spaces in which all closed subsets are homeomorphic to clopen ones,II

A topological spaceX whose topology is the order topology of some linear ordering onX, is called aninterval space. A space in which every closed subspace is homeomorphic to a clopen subspace, is called aCO space and a space isscattered if every non-empty subspace has an isolated point. We regard linear orderings as topological spaces, by equipping them with their order topology. IfL andK are linear orderings, thenL ^*, L+K, L · K denote respectively the reverse ordering ofL, the ordered sum ofL andK and the lexicographic order onL x K (so · 2=+). Ordinals are considered as linear orderings, and cardinals are initial ordinals. For cardinals , l 0, letL(K,)=K+1+*.Theorem: Let X be a compact interval scattered space. Then X is a CO space if and only if X is homeomorphic to a space of the form +1+_{1 L(K i i), where is any ordinal, n , for every ii},_i are regular cardinals and K_ii, and if n>0, then max({K_i:i相似文献   

Arithmetic distance on compact symmetric spaces

Let M be a compact Riemannian symmetric space. Then M=G/K, where G is the identity component of the isometry group of M and K is the isotropy subgroup of G at a point. In 1965 Nagano studied and classified the geometric transformation groups of compact symmetric spaces. Roughly speaking they are larger groups L that act on M, (i) G/L; (ii) L is a Lie transformation group acting effectively on M; (iii) L preserves the symmetric structure of M; and (iv) L is simple.Using Helgason spheres, S(), the minimal totally geodesic spheres in a compact irreducible symmetric space, we define an arithmetic distance for compact irreducible symmetric spaces and prove: THEOREM. Let M=G ^p(K ⁿ ), K=, H, or R, or M=AI(n), of rank greater that 1 and dimension greater that 3, let L be the geometric transformation group of M. Let L={: MM: is a diffeomorphism and preserves arithmetic distance}. Then L=L     

Bessel Potentials with Logarithmic Components and Sobolev-Type Embeddings

In a recent paper Edmunds, Gurka, and Opic [5] showed that Sobolev spaces of order k, based on the Zygmund spaces L ^n/k (log L) (R ⁿ ), are continuously embedded into L (R ⁿ ) if > 1/p, p n/k. In this paper we replace L ^n/k (log L) (R ⁿ ) by the Lebesgue space L ^n/k (R ⁿ ) and increase the smoothness of the functions involved by a "logarithmic" order > 1/p to obtain the continuous embedding into L (R ⁿ ). Both approaches turn out to be equivalent. We also derive results of Trudinger-type [16] on embeddings into Orlicz spaces in the limit case k = n/p as well as results of Brézis-Wainger-type [2] on almost Lipschitz continuity in the superlimiting case k = n/p + 1.     

The transposition of locally compact,connected translation planes

This note deals with the transposition of translation planes in the topological context. We show that a topological congruenceC of the real vector space ²ⁿ has the property that every hyperplane of ²ⁿ contains a component ofC. This makes it possible to define the transposeP of the topological translation planeP associated withC; it is proved that the translation planeP is topological also. The relationship between collineation groups and the relationship between coordinatizing quasifields ofP andP are also discussed.     

Topologische Divisionsalgebren ohne zugehörige topologische affine Ebene

We prove that many (non-associative) topological division algebrasD of dimensionn ∈ N over the centreK do not yield topological affine or projective planes (of Lenz-Barlotti type V) in contrast to the results of SKORNJAKOV [20], SALZMANN [18] and [19], GRUNDHÖFER [7], HARTMANN [11] and RINK [17] concerning projective planes coordinatized by compact or special topological ternary fields. In particular, this holds for every non-trivial and non-archimedian valuation topology ofK distinct from the order topology ifK is a real-closed field, and if the division algebraD =K ⁿ carries the product topology.     

On a class of compact homogeneous spaces I

Le K be a compact connected Lie group, L be a connected closed subgroup of K. It is well known that L is a subgroup of maximal rank of K if and only if the Euler characteristic of the manifold M = K/L is positive. Such homogeneous spaces M have been classified in [7, 10]. However, their topological classification was unknown. This classification is obtained in the present article. We show tha two compact homogeneous spaces M = K/L and M = K/L of positive Euler characteristic are diffeomorphic if and only if the graded rings H ^*(M,Z) and H ^*(M,Z) are isomorphic. We also obtain the rational homotopy classification of such homogeneous spaces which is not equivalent to the differential one. These results were announced in [15].     

Definability properties and the congruence closure

We introduce a natural class of quantifiersTh containing all monadic type quantifiers, all quantifiers for linear orders, quantifiers for isomorphism, Ramsey type quantifiers, and plenty more, showing that no sublogic ofL (Th) or countably compact regular sublogic ofL (Th), properly extendingL , satisfies the uniform reduction property for quotients. As a consequence, none of these logics satisfies either-interpolation or Beth's definability theorem when closed under relativizations. We also show the failure of both properties for any sublogic ofL (Th) in which Chang's quantifier or some cardinality quantifierQ , with 1, is definable.     

Weighted arcs,the finite radon transform and a Ramsey problem

We establish a link between the theory of (k, v)-arcs in affine planes and a graph theoretic Ramsey problem: A (n, k)-coloring of the complete graphK _u is a coloring of the edges ofK _u withk colours such that monochromatic connected subgraphs have at mostn vertices. The Ramsey numberf(n, k) is the smallestu such thatK _u does not admit a (n, k)-coloring. Let be an affine plane of orderq. Aweighted v-arc is a function w: such that line integrals are at mostv. Themass ofw is the sum of all the weights.In certain cases the maximum massM _q (v) can be determined (maximum over all weightedv-arcs and all affine planes of orderq). This yields the exact value off(n, q + 1) for all large enoughn.     

On existence of finite universal Korovkin sets in the centre of group algebras

In this paper, we characterize compact groupsG as well as connected central topological groupsG for which the centreZ(L ¹(G)) admits a finite universal Korovkin set. Also we prove that ifG is a non-connected central topological group which has a compact open normal subgroupK such thatG=KZ, thenZ(L ¹(G)) admits a finite universal Korovkin set if is a finite-dimensional separable metric space or equivalentlyG is separable metrizable andG/K has finite torsion-free rank.     

On the Embedding of an Affine Space into a Projective Space

Let k, K be fields, and assume that |k| 4 and n, m 2, or |k| = 3 and n 3, m 2. Then, for any embedding of AG(n, k) into PG(m, K), there exists an isomorphism from k into K and an (n+1) × (m+1) matrix B with entries in K such that can be expressed as (x₁,x₂,...,x_n) = [(1,x₁ ,x₂ ,...,x_n )B], where the right-hand side is the equivalence class of (1,x₁ ,x₂ ,...,x_n )B. Moreover, in this expression, is uniquely determined, and B is uniquely determined up to a multiplication of element of K*. Let l 1, and suppose that there exists an embedding of AG(m+l, k) into PG(m, K) which has the above expression. If we put r = dim _k K, then we have r 3 and m > 2 l-1)/(r-2). Conversely, there exists an embedding of AG(l+m, k) into PG(m, K) with the above expression if K is a cyclic extension of k with dim _k K=r 3, and if m 2l/(r-2) with m even or if m 2l/(r-2) +1 with m odd.     

The cross-section body, plane sections of convex bodies and approximation of convex bodies, I

For a convex body K ^d we investigate three associated bodies, its intersection body IK (for 0int K), cross-section body CK, and projection body IIK, which satisfy IKCKIIK. Conversely we prove CKconst₁(d)I(K–x) for some xint K, and IIKconst₂ (d)CK, for certain constants, the first constant being sharp. We estimate the maximal k-volume of sections of 1/2(K+(-K)) with k-planes parallel to a fixed k-plane by the analogous quantity for K; our inequality is, if only k is fixed, sharp. For L ^d a convex body, we take n random segments in L, and consider their Minkowski average D. We prove that, for V(L) fixed, the supremum of V(D) (with also nN arbitrary) is minimal for L an ellipsoid. This result implies the Petty projection inequality about max V((IIM)*), for M ^d a convex body, with V(M) fixed. We compare the volumes of projections of convex bodies and the volumes of the projections of their sections, and, dually, the volumes of sections of convex bodies and the volumes of sections of their circumscribed cylinders. For fixed n, the pth moments of V(D) (1p<) also are minimized, for V(L) fixed, by the ellipsoids. For k=2, the supremum (nN arbitrary) and the pth moment (n fixed) of V(D) are maximized for example by triangles, and, for L centrally symmetric, for example by parallelograms. Last we discuss some examples for cross-section bodies.Research (partially) supported by Hungarian National Foundation for Scientific Research, Grant No. 41.     

Tanaka Formulae for (α, d, β)-Superprocesses

We establish Tanaka like formulae for the local time of (, d, )-superprocess in the dimensions where the local time exists. The result generalizes the result of Adler, Lewin who proved existence of Tanaka formulae for a class of super-processes with finite variance. The fact that we abandon the finite variance assumption, requires using an L ¹⁺ convergence argument (with 0<<1) rather than L ² convergence, for the derivation of the Tanaka formulae.     

The Illumination Body of Almost Polygonal Bodies

For a convex body K in R ² with illumination body K we consider an expression connected with the affine surface area of K, namely the volume differences vol₂(K ) - vol₂(K). We investigate what kind of functions can occur as such volume differences and obtain a result similar to the one obtained in the case of floating bodies.     

Affine modifications and affine hypersurfaces with a very transitive automorphism group

We study the modificationAA of an affine domainA which produces another affine domainA=A[I/f] whereI is a nontrivial ideal ofA andf is a nonzero element ofI. First appeared in passing in the basic paper of O. Zariski [Zar], it was further considered by E. D. Davis [Da]. In [Ka1] its geometric counterpart was applied to construct contractible smooth affine varieties non-isomorphic to Euclidean spaces. Here we provide certain conditions (more general than those in [Ka1]) which guarantee preservation of the topology under a modification.As an application, we show that the group of biregular automorphisms of the affine hypersurfaceXC ^k+2, given by the equationuv=(p(x ₁,...,x_k) wherepC[x ₁,...,x _k ],k2, actsm-transitively on the smooth part regX ofX for anymN. We present examples of such hypersurfaces diffeomorphic to Euclidean spaces.Partially supported by the NSA grant MDA904-96-01-0012.     

Tangentially transitive planes of order 16

Lorimer and Rahilly have given constructions for translation planes of order 16. We show that both of these planes have a subplane of order 2 and a group of collineations fixing pointwise which is transitive on the points of –. We show that all such planes of order 16 are isomorphic and that these planes have a number of other properties which are exceptional.     

On the structure of commutative affine group schemes over a non-perfect field

Let k be a non-perfect field of characteristic p>O with a p-basisB and k_s the algebraic separable closure of k. Starting from the ring of Schoeller D ^B [3] and the topological Galois group II of k_s over k, we construct a new ring such that the category of commutative affine k-group schemes is anti-equivalent to the category ofeffaceable left -modules. (The effaceability is defined in the text).     

Patching ideal families on℘ kλ

Ideal families defined on a cardinalk often exhibit reflection properties. IfC k is a club, for example, thenC is a club-in- club-in-k often. In this paper we generalize this notion to ideal families defined on _k and exhibit some examples.     

On a class of Hankel operators: Fredholm properties and invertibility

A study is presented on the Fredholm properties and invertibility of a Hankel integral operator inL ₊ ² () with a kernel function inS whose Fourier transformK is a measurable essentially bounded function in . This study is based on the properties of a Wiener-Hopf operator with a matrix valued symbol naturally associated with the operator mentioned above. Further results are obtained for the case whereK PC(), and an application to a diffraction problem is presented.