منابع مشابه
Indecomposable Pd 3 - Complexes
We show that if X is an indecomposable P D 3-complex and π 1 (X) is the fundamental group of a reduced finite graph of finite groups but is neither Z nor Z ⊕ Z/2Z then X is orientable, the underlying graph is a tree, the vertex groups have cohomolog-ical period dividing 4 and all but at most one of the edge groups is Z/2Z. If there are no exceptions then all but at most one of the vertex groups...
متن کامل00 8 Indecomposable Pd 3 - Complexes
We show that if the fundamental group π of an inde-composable orientable P D 3-complex is the fundamental group of a finite graph of finite groups then the vertex groups have periodic cohomology and the edge groups are metacyclic. If the vertex groups all have cohomological period dividing 4 at most one is not dihedral, the edge groups are Z/2Z, and the underlying graph is a tree. We also ask w...
متن کاملIndecomposable Polytopes
The space of summands (with respect to vector addition) of a convex polytope in n dimensions is studied. This space is shown to be isomorphic to a convex pointed cone in Euclidean space. The extreme rays of this cone correspond to similarity classes of indecomposable polytopes. The decomposition of a polytope is described and a bound is given for the number of indecomposable summands needed. A ...
متن کاملIndecomposable Coverings
We prove that for every k > 1, there exist k-fold coverings of the plane (1) with strips, (2) with axis-parallel rectangles, and (3) with homothets of any fixed concave quadrilateral, that cannot be decomposed into two coverings. We also construct, for every k > 1, a set of points P and a family of disks D in the plane, each containing at least k elements of P , such that no matter how we color...
متن کاملIndecomposable Cones
We study some relations between a reproducing cone K in a linear space V over a fully ordered field F and the cone I(K) in Hom( V, V) consisting of all operators A such that AK G K. In particular, indecomposable cones are considered.
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ژورنال
عنوان ژورنال: Journal of Combinatorial Theory, Series A
سال: 1991
ISSN: 0097-3165
DOI: 10.1016/0097-3165(91)90019-d