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Polygons as sections of higherdimensional polytopes
(20150209)
Article
Open AccessWe show that every heptagon is a section of a 3polytope with 6 vertices. This implies that every ngon with n >= 7 can be obtained as a section of a (2 + [n/7])dimensional polytope with at most [6n/7] vertices; and ... 
Lower bounds on the maximum number of noncrossing acyclic graphs
(20150801)
Article
Restricted access  publisher's policyThis paper is a contribution to the problem of counting geometric graphs on point sets. More concretely, we look at the maximum numbers of noncrossing spanning trees and forests. We show that the socalled double chain ... 
Finite automata for Schreier graphs of virtually free groups
(20160101)
Article
Restricted access  publisher's policyThe Stallings construction for f.g. subgroups of free groups is generalized by introducing the concept of Stallings section, which allows efficient computation of the core of a Schreier graph based on edge folding. It is ... 
On the probability of planarity of a random graph near the critical point
(20150301)
Article
Open AccessLet G(n, M) be the uniform random graph with n vertices and M edges. Erdos and Renyi (1960) conjectured that the limiting probability; lim(n >infinity) Pr{G(n, n/2) is planar}; exists and is a constant strictly between 0 ... 
The automorphism group of a freebycyclic group in rank 2
(200705)
Article
Open AccessLet ¡ be an automorphism of a free group F 2 of rank 2 and let M ¡ = F 2 o ¡ Z be the corresponding mapping torus of ¡ . We prove that the group Out ( M ¡ ) is usually virtually cyclic. More over, ... 
Absolutetype shaft encoding using LFSR sequences with a prescribed length
(20080331)
Article
Open AccessMaximallength binary sequences have existed for a long time. They have many interesting properties, and one of them is that, when taken in blocks of n consecutive positions, they form 2n  1 different codes in a closed ... 
Absolute type shaft encoding using LFSR sequences with prescribed length
(200602)
Article
Open AccessMaximallength binary sequences have been known for a long time. They have many interesting properties, one of them is that when taken in blocks of n consecutive positions they form 2 n ° 1 diÆerent codes in a ... 
Completion and decomposition of a clutter into representable matroids
(Elsevier, 20150501)
Article
Restricted access  publisher's policyThis paper deals with the question of completing a monotone increasing family of subsets Gamma of a finite set Omega to obtain the linearly dependent subsets of a family of vectors of a vector space. Specifically, we prove ... 
Fixed subgroups are compressed in surface groups
(20150801)
Article
Restricted access  publisher's policyFor a compact surface Sigma (orientable or not, and with boundary or not), we show that the fixed subgroup, Fix B, of any family B of endomorphisms of pi(1)(Sigma) is compressed in pi(1)(Sigma), i.e. rk(Fix B) <= rk(H) for ... 
Extensions and presentations of transversal matroids
(20151102)
Article
Restricted access  publisher's policyA transversal matroid MM can be represented by a collection of sets, called a presentation of MM, whose partial transversals are the independent sets of MM. Minimal presentations are those for which removing any element ...