Let M and N be internally 4-connected binary matroids such that M has a proper N-minor, and |E(N)| is at least seven. As part of our project to develop a splitter theorem for internally 4-connected binary matroids, we prove the following result: if M\e has no N-minor whenever e is in a triangle of M, and M/e has no N-minor whenever e is in a triad of M, then M has a minor, M', such that M' is internally 4-connected with an N-minor, and 0 < |E(M)|-|E(M')| < 3.

Carolyn Chun Dillon Mayhew James Oxley

Given a von Neumann algebra $M$ we consider the central extension $E(M)$ of $M.$ We introduce the topology $t_c(M)$ on $E(M)$ generated by a center-valued norm and prove that it coincides with the topology of convergence locally in measure on $E(M)$ if and only if $M$ does not have direct summands of type II. We also show that $t_c(M)$ restricted on the set $E(M)_h$ of self-adjoint elements of $E(M)$ coincides with the order topology on $E(M)_h$ if and only if $M$ is a $\sigma$-finite type I$_{fin}$ von Neumann algebra.

Sh. A. Ayupov K. K. Kudaybergenov R. T. Djumamuratov

The Coupon Collector's Problem is one of the few mathematical problems that make news headlines regularly. The reasons for this are on one hand the immense popularity of soccer albums (called Paninimania) and on the other hand that no solution is known that is able to take into account all effects such as replacement (limited purchasing of missing stickers) or swapping. In previous papers we have proven that the classical assumptions are not fulfilled in practice. Therefore we define new assumptions that match reality. Based on these assumptions we are able to derive formulae for the mean number of stickers needed (and the associated standard deviation) that are able to take into account all effects that occur in practical collecting. Thus collectors can estimate the average cost of completion of an album and its standard deviation just based on elementary calculations. From a practical point of view we consider the Coupon Collector's problem as solved. ----- Das Sammelbilderproblem ist eines der wenigen mathematischen Probleme, die regelm\"a{\ss}ig in den Schlagzeilen der Nachrichten vorkommen. Dies liegt einerseits an der gro{\ss}en Popularit\"at von Fu{\ss}ball-Sammelbildern (Paninimania genannt) und andererseits daran, dass es bisher keine L\"osung gibt, die alle relevanten Effekte wie Nachkaufen oder Tauschen ber\"ucksichtigt. Wir haben bereits nachgewiesen, dass die klassischen Annahmen nicht der Realit\"at entsprechen. Deshalb stellen wir neue Annahmen auf, die die Praxis besser abbilden. Darauf aufbauend k\"onnen wir Formeln f\"ur die mittlere Anzahl ben\"otigter Bilder (sowie deren Standardabweichung) ableiten, die alle in der Praxis relevanten Effekte ber\"ucksichtigen. Damit k\"onnen Sammler die mittleren Kosten eines Albums sowie deren Standardabweichung nur mit Hilfe von elementaren Rechnungen bestimmen. F\"ur praktische Zwecke ist das Sammelbilderproblem damit gel\"ost.

Niklas Braband Sonja Braband Malte Braband

We prove a Lie-algebraic characterization of vector bundle for the Lie algebra $\mathcal{D}(E,M),$ seen as ${\rm C}^\infty(M)-$module, of all linear operators acting on sections of a vector bundle $E\to M$. We obtain similar result for its Lie subalgebra $\mathcal{D}^1(E,M)$ of all linear first-order differential operators. Thanks to a well-chosen filtration, $\mathcal{D}(E,M)$ becomes $\mathcal{P}(E,M)$ and we prove that $\mathcal{P}^1(E,M)$ characterizes the vector bundle without the hypothesis of being seen as ${\rm C}^\infty(M)-$module. We prove that the Lie algebra $\mathcal{S}(\mathcal{P}(E,M))$ of symbols of linear operators acting on smooth sections of a vector bundle $E\to M,$ characterizes it. To obtain this, we assume that $\mathcal{S}(\mathcal{P}(E,M))$ is seen as ${\rm C}^\infty(M)-$module. We obtain a similar result with the Lie algebra $\mathcal{S}^1(\mathcal{P}(E,M))$ of symbols of first-order linear operators without the hypothesis of being seen as a ${\rm C}^\infty(M)-$module.

Pierre B. A. Lecomte Elie Zihindula Mushengezi

Let $E$ be a primarily quasilocal field, $M/E$ a finite Galois extension and $D$ a central division $E$-algebra of index divisible by $[M\colon E]$. In addition to the main result of Part I, this part of the paper shows that if the Galois group $G(M/E)$ is not nilpotent, then $M$ does not necessarily embed in $D$ as an $E$-subalgebra. When $E$ is quasilocal, we find the structure of the character group of its absolute Galois group; this enables us to prove that if $E$ is strictly quasilocal and almost perfect, then the divisible part of the multiplicative group $E ^{\ast}$ equals the intersection of the norm groups of finite Galois extensions of $E$.

I. D. Chipchakov

Given a 3-hypergraph $H$, a subset $M$ of $V(H)$ is a module of $H$ if for each $e\in E(H)$ such that $e\cap M\neq\emptyset$ and $e\setminus M\neq\emptyset$, there exists $m\in M$ such that $e\cap M=\{m\}$ and for every $n\in M$, we have $(e\setminus\{m\})\cup\{n\}\in E(H)$. For example, $\emptyset$, $V(H)$ and $\{v\}$, where $v\in V(H)$, are modules of $H$, called trivial. A 3-hypergraph is prime if all its modules are trivial. Furthermore, a prime 3-hypergraph is critical if all its induced subhypergraphs, obtained by removing one vertex, are not prime. We characterize the critical 3-hypergraphs.

Abderrahim Boussairi Brahim Chergui Pierre Ille Mohamed Zaidi

Let $M$ be a 3-connected binary matroid and let $Y(M)$ be the set of elements of $M$ avoiding at least $r(M)+1$ non-separating cocircuits of $M$. Lemos proved that $M$ is non-graphic if and only if $Y(M)\neq\emp$. We generalize this result when by establishing that $Y(M)$ is very large when $M$ is non-graphic and $M$ has no $M\s(K_{3,3}"')$-minor if $M$ is regular. More precisely that $|E(M)-Y(M)|\le 1$ in this case. We conjecture that when $M$ is a regular matroid with an $M\s(K_{3,3})$-minor, then $r\s_M(E(M)-Y(M))\le 2$. The proof of such conjecture is reduced to a computational verification.

João Paulo Costalonga

We prove that every weak-local triple derivation on a JB$^*$-triple $E$ (i.e. a linear map $T: E\to E$ such that for each $\phi \in E^*$ and each $a\in E$, there exists a triple derivation $\delta_{a,\phi} : E\to E$, depending on $\phi$ and $a$, such that $\phi T(a) = \phi \delta_{a,\phi} (a)$) is a (continuous) triple derivation.

M. J. Burgos J. C. Cabello A. M. Peralta

Let $A$ be a $m\times m$ complex matrix with zero trace and let $\e>0$. Then there are $m\times m$ matrices $B$ and $C$ such that $A=[B,C]$ and $\|B\|\|C\|\le K_\e m^\e\|A\|$ where $K_\e$ depends only on $\e$. Moreover, the matrix $B$ can be taken to be normal.

William B. Johnson Narutaka Ozawa Gideon Schechtman

Suppose M is a connected PL 2-manifold and X is a compact connected subpolyhedron of M (X \neq 1pt, a closed 2-manifold). Let E(X, M) denote the space of topological embeddings of X into M with the compact-open topology and let E(X, M)_0 denote the connected component of the inclusion i_X : X \subset M in E(X, M). In this paper we classify the homotopy type of E(X, M)_0 in term of the subgroup G = Im[{i_X}_\ast : \pi_1(X) \to \pi_1(M)]. We show that if G is not a cyclic group and M \neq T^2, T^2 then E(X, M)_0 \simeq \ast, if G is a nontrivial cyclic group and M \neq P^2, T^2, K^2 then E(X, M)_0 \simeq S^1, and when G = 1, if X is an arc or M is orientable then E(X, M)_0 \simeq ST(M) and if X is not an arc and M is nonorientable then E(X, M)_0 \simeq ST(\tilde{M}). Here S^1 is the circle, T^2 is the torus, P^2 is the projective plane and K^2 is the Klein bottle. The symbol ST(M) denotes the tangent unit circle bundle of M with respect to any Riemannian metric of M and \tilde{M} denotes the orientation double cover of M.

Tatsuhiko Yagasaki