90101 Pure Mathematics
40802 Computation Theory and Mathematics
4Polytopes
30103 Numerical and Computational Mathematics
3Banach space
201 Mathematical Sciences
2F-vector
2Polytope
2Reconstruction
2Simple polytope
2k-Skeleton
10102 Applied Mathematics
10104 Statistics
113 Education
12005 Literary Studies
13 space problem
152B05 (Secondary)
152B10
152B11 (Primary)
1Algorithms

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A Different Johnson-Lindenstrauss Space

**Authors:**Yost, David**Date:**2008**Type:**Text , Journal article**Relation:**New Zealand Journal of Mathematics Vol. 37, no. (2008), p. 47-49**Full Text:**false**Reviewed:****Description:**We exhibit a non-trivial twisted sum of c0 with a Hilbert space, which is not isomorphic to the example constructed by Johnson and Lindenstrauss in 1974. In fact, no non-separable subspace of either example is isomorphic to any subspace of the other.**Description:**2003006488

Almost simplicial polytopes : the lower and upper bound theorems

- Nevo, Eran, Pineda-Villavicencio, Guillermo, Ugon, Julien, Yost, David

**Authors:**Nevo, Eran , Pineda-Villavicencio, Guillermo , Ugon, Julien , Yost, David**Date:**2020**Type:**Text , Journal article**Relation:**Canadian Journal of Mathematics Vol. 72, no. 2 (2020), p. 537-556. http://purl.org/au-research/grants/arc/DP180100602**Full Text:****Reviewed:****Description:**We study -vertex -dimensional polytopes with at most one nonsimplex facet with, say, vertices, called almost simplicial polytopes. We provide tight lower and upper bound theorems for these polytopes as functions of, and, thus generalizing the classical Lower Bound Theorem by Barnette and the Upper Bound Theorem by McMullen, which treat the case where s = 0. We characterize the minimizers and provide examples of maximizers for any. Our construction of maximizers is a generalization of cyclic polytopes, based on a suitable variation of the moment curve, and is of independent interest. © 2018 Canadian Mathematical Society.

**Authors:**Nevo, Eran , Pineda-Villavicencio, Guillermo , Ugon, Julien , Yost, David**Date:**2020**Type:**Text , Journal article**Relation:**Canadian Journal of Mathematics Vol. 72, no. 2 (2020), p. 537-556. http://purl.org/au-research/grants/arc/DP180100602**Full Text:****Reviewed:****Description:**We study -vertex -dimensional polytopes with at most one nonsimplex facet with, say, vertices, called almost simplicial polytopes. We provide tight lower and upper bound theorems for these polytopes as functions of, and, thus generalizing the classical Lower Bound Theorem by Barnette and the Upper Bound Theorem by McMullen, which treat the case where s = 0. We characterize the minimizers and provide examples of maximizers for any. Our construction of maximizers is a generalization of cyclic polytopes, based on a suitable variation of the moment curve, and is of independent interest. © 2018 Canadian Mathematical Society.

Chebyshev multivariate polynomial approximation and point reduction procedure

- Sukhorukova, Nadezda, Ugon, Julien, Yost, David

**Authors:**Sukhorukova, Nadezda , Ugon, Julien , Yost, David**Date:**2021**Type:**Text , Journal article**Relation:**Constructive Approximation Vol. 53, no. 3 (2021), p. 529-544**Relation:**http://purl.org/au-research/grants/arc/DP180100602**Full Text:****Reviewed:****Description:**We apply the methods of nonsmooth and convex analysis to extend the study of Chebyshev (uniform) approximation for univariate polynomial functions to the case of general multivariate functions (not just polynomials). First of all, we give new necessary and sufficient optimality conditions for multivariate approximation, and a geometrical interpretation of them which reduces to the classical alternating sequence condition in the univariate case. Then, we present a procedure for verification of necessary and sufficient optimality conditions that is based on our generalization of the notion of alternating sequence to the case of multivariate polynomials. Finally, we develop an algorithm for fast verification of necessary optimality conditions in the multivariate polynomial case. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.

**Authors:**Sukhorukova, Nadezda , Ugon, Julien , Yost, David**Date:**2021**Type:**Text , Journal article**Relation:**Constructive Approximation Vol. 53, no. 3 (2021), p. 529-544**Relation:**http://purl.org/au-research/grants/arc/DP180100602**Full Text:****Reviewed:****Description:**We apply the methods of nonsmooth and convex analysis to extend the study of Chebyshev (uniform) approximation for univariate polynomial functions to the case of general multivariate functions (not just polynomials). First of all, we give new necessary and sufficient optimality conditions for multivariate approximation, and a geometrical interpretation of them which reduces to the classical alternating sequence condition in the univariate case. Then, we present a procedure for verification of necessary and sufficient optimality conditions that is based on our generalization of the notion of alternating sequence to the case of multivariate polynomials. Finally, we develop an algorithm for fast verification of necessary optimality conditions in the multivariate polynomial case. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.

Colocality and twisted sums of Banach spaces

- Jebreen, H. M., Jamjoom, F. B. H., Yost, David

**Authors:**Jebreen, H. M. , Jamjoom, F. B. H. , Yost, David**Date:**2006**Type:**Text , Journal article**Relation:**Journal of Mathematical Analysis and Applications Vol. 323, no. 2 (2006), p. 864-875**Full Text:****Reviewed:****Description:**Using the relation between subspaces of Banach spaces and quotients of their duals, we introduce the concept of colocality to give a new method that guarantees the existence of nontrivial twisted sums in which finite quotients play a major role (Theorem 1.7). An interesting point is that no restrictions are imposed on the quotients, only on the various subspaces. New examples of nontrivial twisted sums are given.**Description:**C1**Description:**2003001831

**Authors:**Jebreen, H. M. , Jamjoom, F. B. H. , Yost, David**Date:**2006**Type:**Text , Journal article**Relation:**Journal of Mathematical Analysis and Applications Vol. 323, no. 2 (2006), p. 864-875**Full Text:****Reviewed:****Description:**Using the relation between subspaces of Banach spaces and quotients of their duals, we introduce the concept of colocality to give a new method that guarantees the existence of nontrivial twisted sums in which finite quotients play a major role (Theorem 1.7). An interesting point is that no restrictions are imposed on the quotients, only on the various subspaces. New examples of nontrivial twisted sums are given.**Description:**C1**Description:**2003001831

Decomposability of polytopes

- Przeslawski, Krzysztof, Yost, David

**Authors:**Przeslawski, Krzysztof , Yost, David**Date:**2008**Type:**Text , Journal article**Relation:**Discrete & Computational Geometry Vol. 39, no. 1-3 (Mar 2008), p. 460-468**Full Text:****Reviewed:****Description:**A known characterization of the decomposability of polytopes is reformulated in a way which may be more computationally convenient, and a more transparent proof is given. New sufficient conditions for indecomposability are then deduced, and illustrated with some examples.**Description:**C1

**Authors:**Przeslawski, Krzysztof , Yost, David**Date:**2008**Type:**Text , Journal article**Relation:**Discrete & Computational Geometry Vol. 39, no. 1-3 (Mar 2008), p. 460-468**Full Text:****Reviewed:****Description:**A known characterization of the decomposability of polytopes is reformulated in a way which may be more computationally convenient, and a more transparent proof is given. New sufficient conditions for indecomposability are then deduced, and illustrated with some examples.**Description:**C1

Extending of L-infinity-valued operators under a twisted light

- Cabello Sanchez, Felix, Castillo, Jesus, Moreno, Y, Yost, David

**Authors:**Cabello Sanchez, Felix , Castillo, Jesus , Moreno, Y , Yost, David**Date:**2002**Type:**Text , Conference paper**Relation:**Paper presented at Functional analysis and its applications. Proceedings of the International Conference. dedicated to the 110th anniversary of Stefan Banach, Lviv, Ukraine : 28th - 31st May, 2002 p. 59-70**Full Text:****Reviewed:****Description:**E1

**Authors:**Cabello Sanchez, Felix , Castillo, Jesus , Moreno, Y , Yost, David**Date:**2002**Type:**Text , Conference paper**Relation:**Paper presented at Functional analysis and its applications. Proceedings of the International Conference. dedicated to the 110th anniversary of Stefan Banach, Lviv, Ukraine : 28th - 31st May, 2002 p. 59-70**Full Text:****Reviewed:****Description:**E1

Integration: Reversing traditional pedagogy

**Authors:**Yost, David**Date:**2008**Type:**Text , Journal article**Relation:**Australian Senior Mathematics Journal Vol. 22, no. 2 (2008), p. 37-40**Full Text:**false**Reviewed:****Description:**The author recommends teaching integration first, and move on to differential calculus only after a sound understanding of integration has been attained. A rationale for teaching integrals before derivatives in a first calculus unit intended primarily for engineering students at the University of Ballarat is presented. It is concluded that students fail to see the connection between getting the right answer and understanding what they are doing. It is noted that the formal manipulations required for high school differential calculus questions are simpler than those for integral calculus.

Lipschitz selections for multifunctions

**Authors:**Yost, David**Date:**2010**Type:**Text , Conference proceedings**Full Text:**false

Lower bound theorems for general polytopes

- Pineda-Villavicencio, Guillermo, Ugon, Julien, Yost, David

**Authors:**Pineda-Villavicencio, Guillermo , Ugon, Julien , Yost, David**Date:**2019**Type:**Text , Journal article**Relation:**European Journal of Combinatorics Vol. 79, no. (2019), p. 27-45**Full Text:****Reviewed:****Description:**For a d-dimensional polytope with v vertices, d + 1 <= v <= 2d, we calculate precisely the minimum possible number of m-dimensional faces, when m = 1 or m >= 0.62d. This confirms a conjecture of Grunbaum, for these values of m. For v = 2d + 1, we solve the same problem when m = 1 or d - 2; the solution was already known for m = d - 1. In all these cases, we give a characterisation of the minimising polytopes. We also show that there are many gaps in the possible number of m-faces: for example, there is no polytope with 80 edges in dimension 10, and a polytope with 407 edges can have dimension at most 23.

**Authors:**Pineda-Villavicencio, Guillermo , Ugon, Julien , Yost, David**Date:**2019**Type:**Text , Journal article**Relation:**European Journal of Combinatorics Vol. 79, no. (2019), p. 27-45**Full Text:****Reviewed:****Description:**For a d-dimensional polytope with v vertices, d + 1 <= v <= 2d, we calculate precisely the minimum possible number of m-dimensional faces, when m = 1 or m >= 0.62d. This confirms a conjecture of Grunbaum, for these values of m. For v = 2d + 1, we solve the same problem when m = 1 or d - 2; the solution was already known for m = d - 1. In all these cases, we give a characterisation of the minimising polytopes. We also show that there are many gaps in the possible number of m-faces: for example, there is no polytope with 80 edges in dimension 10, and a polytope with 407 edges can have dimension at most 23.

More indecomposable polyhedra

- Przesławski, Krzysztof, Yost, David

**Authors:**Przesławski, Krzysztof , Yost, David**Date:**2016**Type:**Text , Journal article**Relation:**Extracta Mathematicae Vol. 31, no. 2 (2016), p. 169-188**Full Text:****Reviewed:****Description:**We apply combinatorial methods to a geometric problem: the classification of polytopes, in terms of Minkowski decomposability. Various properties of skeletons of polytopes are exhibited, each sufficient to guarantee indecomposability of a significant class of polytopes. We illustrate further the power of these techniques, compared with the traditional method of examining triangular faces, with several applications. In any dimension d 6= 2, we show that of all the polytopes with d2 + 1 2 d or fewer edges, only one is decomposable. In 3 dimensions, we complete the classification, in terms of decomposability, of the 260 combinatorial types of polyhedra with 15 or fewer edges.**Description:**We apply combinatorial methods to a geometric problem: the classification of polytopes, in terms of Minkowski decomposability. Various properties of skeletons of polytopes are exhibited, each sufficient to guarantee indecomposability of a significant class of polytopes. We illustrate further the power of these techniques, compared with the traditional method of examining triangular faces, with several applications. In any dimension $d\neq 2$, we show that of all the polytopes with $d^2+\frac{d}{2}$ or fewer edges, only one is decomposable. In 3 dimensions, we complete the classification, in terms of decomposability, of the 260 combinatorial types of polyhedra with 15 or fewer edges.

**Authors:**Przesławski, Krzysztof , Yost, David**Date:**2016**Type:**Text , Journal article**Relation:**Extracta Mathematicae Vol. 31, no. 2 (2016), p. 169-188**Full Text:****Reviewed:****Description:**We apply combinatorial methods to a geometric problem: the classification of polytopes, in terms of Minkowski decomposability. Various properties of skeletons of polytopes are exhibited, each sufficient to guarantee indecomposability of a significant class of polytopes. We illustrate further the power of these techniques, compared with the traditional method of examining triangular faces, with several applications. In any dimension d 6= 2, we show that of all the polytopes with d2 + 1 2 d or fewer edges, only one is decomposable. In 3 dimensions, we complete the classification, in terms of decomposability, of the 260 combinatorial types of polyhedra with 15 or fewer edges.**Description:**We apply combinatorial methods to a geometric problem: the classification of polytopes, in terms of Minkowski decomposability. Various properties of skeletons of polytopes are exhibited, each sufficient to guarantee indecomposability of a significant class of polytopes. We illustrate further the power of these techniques, compared with the traditional method of examining triangular faces, with several applications. In any dimension $d\neq 2$, we show that of all the polytopes with $d^2+\frac{d}{2}$ or fewer edges, only one is decomposable. In 3 dimensions, we complete the classification, in terms of decomposability, of the 260 combinatorial types of polyhedra with 15 or fewer edges.

Observations on the separable quotient problem for banach spaces

**Authors:**Morris, Sidney , Yost, David**Date:**2020**Type:**Text , Journal article**Relation:**Axioms Vol. 9, no. 1 (2020), p.**Full Text:****Reviewed:****Description:**The longstanding Banach-Mazur separable quotient problem asks whether every infinite-dimensional Banach space has a quotient (Banach) space that is both infinite-dimensional and separable. Although it remains open in general, an affirmative answer is known in many special cases, including (1) reflexive Banach spaces, (2) weakly compactly generated (WCG) spaces, and (3) Banach spaces which are dual spaces. Obviously (1) is a special case of both (2) and (3), but neither (2) nor (3) is a special case of the other. A more general result proved here includes all three of these cases. More precisely, we call an infinite-dimensional Banach space X dual-like, if there is another Banach space E, a continuous linear operator T from the dual space E* onto a dense subspace of X, such that the closure of the kernel of T (in the relative weak* topology) has infinite codimension in E*. It is shown that every dual-like Banach space has an infinite-dimensional separable quotient. © 2020 by the authors.

**Authors:**Morris, Sidney , Yost, David**Date:**2020**Type:**Text , Journal article**Relation:**Axioms Vol. 9, no. 1 (2020), p.**Full Text:****Reviewed:****Description:**The longstanding Banach-Mazur separable quotient problem asks whether every infinite-dimensional Banach space has a quotient (Banach) space that is both infinite-dimensional and separable. Although it remains open in general, an affirmative answer is known in many special cases, including (1) reflexive Banach spaces, (2) weakly compactly generated (WCG) spaces, and (3) Banach spaces which are dual spaces. Obviously (1) is a special case of both (2) and (3), but neither (2) nor (3) is a special case of the other. A more general result proved here includes all three of these cases. More precisely, we call an infinite-dimensional Banach space X dual-like, if there is another Banach space E, a continuous linear operator T from the dual space E* onto a dense subspace of X, such that the closure of the kernel of T (in the relative weak* topology) has infinite codimension in E*. It is shown that every dual-like Banach space has an infinite-dimensional separable quotient. © 2020 by the authors.

On the reconstruction of polytopes

- Doolittle, Joseph, Nevo, Eran, Pineda-Villavicencio, Guillermo, Ugon, Julien, Yost, David

**Authors:**Doolittle, Joseph , Nevo, Eran , Pineda-Villavicencio, Guillermo , Ugon, Julien , Yost, David**Date:**2019**Type:**Text , Journal article**Relation:**Discrete and Computational Geometry Vol. 61, no. 2 (2019), p. 285-302. http://purl.org/au-research/grants/arc/DP180100602**Full Text:****Reviewed:****Description:**Blind and Mani, and later Kalai, showed that the face lattice of a simple polytope is determined by its graph, namely its 1-skeleton. Call a vertex of a d-polytope nonsimple if the number of edges incident to it is more than d. We show that (1) the face lattice of any d-polytope with at most two nonsimple vertices is determined by its 1-skeleton; (2) the face lattice of any d-polytope with at most d- 2 nonsimple vertices is determined by its 2-skeleton; and (3) for any d> 3 there are two d-polytopes with d- 1 nonsimple vertices, isomorphic (d- 3) -skeleta and nonisomorphic face lattices. In particular, the result (1) is best possible for 4-polytopes. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.

**Authors:**Doolittle, Joseph , Nevo, Eran , Pineda-Villavicencio, Guillermo , Ugon, Julien , Yost, David**Date:**2019**Type:**Text , Journal article**Relation:**Discrete and Computational Geometry Vol. 61, no. 2 (2019), p. 285-302. http://purl.org/au-research/grants/arc/DP180100602**Full Text:****Reviewed:****Description:**Blind and Mani, and later Kalai, showed that the face lattice of a simple polytope is determined by its graph, namely its 1-skeleton. Call a vertex of a d-polytope nonsimple if the number of edges incident to it is more than d. We show that (1) the face lattice of any d-polytope with at most two nonsimple vertices is determined by its 1-skeleton; (2) the face lattice of any d-polytope with at most d- 2 nonsimple vertices is determined by its 2-skeleton; and (3) for any d> 3 there are two d-polytopes with d- 1 nonsimple vertices, isomorphic (d- 3) -skeleta and nonisomorphic face lattices. In particular, the result (1) is best possible for 4-polytopes. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.

Polytopes close to being simple

- Pineda-Villavicencio, Guillermo, Ugon, Julien, Yost, David

**Authors:**Pineda-Villavicencio, Guillermo , Ugon, Julien , Yost, David**Date:**2020**Type:**Text , Journal article**Relation:**Discrete and Computational Geometry Vol. 64, no. 1 (2020), p. 200-215**Full Text:****Reviewed:****Description:**It is known that polytopes with at most two nonsimple vertices are reconstructible from their graphs, and that d-polytopes with at most d- 2 nonsimple vertices are reconstructible from their 2-skeletons. Here we close the gap between 2 and d- 2 , showing that certain polytopes with more than two nonsimple vertices are reconstructible from their graphs. In particular, we prove that reconstructibility from graphs also holds for d-polytopes with d+ k vertices and at most d- k+ 3 nonsimple vertices, provided k

**Authors:**Pineda-Villavicencio, Guillermo , Ugon, Julien , Yost, David**Date:**2020**Type:**Text , Journal article**Relation:**Discrete and Computational Geometry Vol. 64, no. 1 (2020), p. 200-215**Full Text:****Reviewed:****Description:**It is known that polytopes with at most two nonsimple vertices are reconstructible from their graphs, and that d-polytopes with at most d- 2 nonsimple vertices are reconstructible from their 2-skeletons. Here we close the gap between 2 and d- 2 , showing that certain polytopes with more than two nonsimple vertices are reconstructible from their graphs. In particular, we prove that reconstructibility from graphs also holds for d-polytopes with d+ k vertices and at most d- k+ 3 nonsimple vertices, provided k

Quasilinear Mappings, M-Ideals and Popyhedra

**Authors:**Yost, David**Date:**2012**Type:**Text , Conference paper**Relation:**Operators and Matrices Vol. 6, p. 279-286**Full Text:****Reviewed:****Description:**We survey the connection between two results from rather different areas: failure of the 3-space property for local convexity (and other properties) within the category of quasi-Banach spaces, and the irreducibility (in the sense of Minkowski difference) of large families of finite dimensional polytopes.**Description:**C1

**Authors:**Yost, David**Date:**2012**Type:**Text , Conference paper**Relation:**Operators and Matrices Vol. 6, p. 279-286**Full Text:****Reviewed:****Description:**We survey the connection between two results from rather different areas: failure of the 3-space property for local convexity (and other properties) within the category of quasi-Banach spaces, and the irreducibility (in the sense of Minkowski difference) of large families of finite dimensional polytopes.**Description:**C1

Reducible polytopes

**Authors:**Yost, David**Date:**2005**Type:**Text , Conference paper**Relation:**Paper presented at the Sixteenth Australasian Workshop on Combinatorial Algorithms, 18-21 September 2005, Ballarat, Australia, Ballarat, Victoria : 18th - 21st September, 2005**Full Text:****Reviewed:****Description:**E1**Description:**2003001436

**Authors:**Yost, David**Date:**2005**Type:**Text , Conference paper**Relation:**Paper presented at the Sixteenth Australasian Workshop on Combinatorial Algorithms, 18-21 September 2005, Ballarat, Australia, Ballarat, Victoria : 18th - 21st September, 2005**Full Text:****Reviewed:****Description:**E1**Description:**2003001436

Some indecomposable polyhedra

**Authors:**Yost, David**Date:**2007**Type:**Text , Journal article**Relation:**Optimization Vol. 56, no. 5-6 (2007), p. 715-724**Full Text:****Reviewed:****Description:**We complete the classification, in terms of decomposability, of all combinatorial types of polytopes with 14 or fewer edges. Recall that a polytope P is said to be decomposable if it is equal to a Minkowski sum [image omitted] of two polytopes Q and R which are not similar to P. Our main contribution here is to consider the 42 types of polyhedra with 8 faces and 8 vertices. It turns out that 34 of these are always indecomposable, and 5 are always decomposable. The remaining 3 are ambiguous, i.e. each of them has both decomposable and indecomposable geometric realizations.**Description:**C1**Description:**2003004904

**Authors:**Yost, David**Date:**2007**Type:**Text , Journal article**Relation:**Optimization Vol. 56, no. 5-6 (2007), p. 715-724**Full Text:****Reviewed:****Description:**We complete the classification, in terms of decomposability, of all combinatorial types of polytopes with 14 or fewer edges. Recall that a polytope P is said to be decomposable if it is equal to a Minkowski sum [image omitted] of two polytopes Q and R which are not similar to P. Our main contribution here is to consider the 42 types of polyhedra with 8 faces and 8 vertices. It turns out that 34 of these are always indecomposable, and 5 are always decomposable. The remaining 3 are ambiguous, i.e. each of them has both decomposable and indecomposable geometric realizations.**Description:**C1**Description:**2003004904

The excess degree of a polytope

- Pineda-Villavicencio, Guillermo, Ugon, Julien, Yost, David

**Authors:**Pineda-Villavicencio, Guillermo , Ugon, Julien , Yost, David**Date:**2018**Type:**Text , Journal article**Relation:**SIAM Journal on Discrete Mathematics Vol. 32, no. 3 (2018), p. 2011-2046, http://purl.org/au-research/grants/arc/DP180100602**Full Text:****Reviewed:****Description:**We define the excess degree \xi (P) of a d-polytope P as 2f1 - df0, where f0 and f1 denote the number of vertices and edges, respectively. This parameter measures how much P deviates from being simple. It turns out that the excess degree of a d-polytope does not take every natural number: the smallest possible values are 0 and d - 2, and the value d - 1 only occurs when d = 3 or 5. On the other hand, for fixed d, the number of values not taken by the excess degree is finite if d is odd, and the number of even values not taken by the excess degree is finite if d is even. The excess degree is then applied in three different settings. First, it is used to show that polytopes with small excess (i.e., \xi (P) < d) have a very particular structure: provided d ot = 5, either there is a unique nonsimple vertex, or every nonsimple vertex has degree d + 1. This implies that such polytopes behave in a similar manner to simple polytopes in terms of Minkowski decomposability: they are either decomposable or pyramidal, and their duals are always indecomposable. Second, we characterize completely the decomposable d-polytopes with 2d + 1 vertices (up to combinatorial equivalence). Third, all pairs (f0, f1), for which there exists a 5-polytope with f0 vertices and f1 edges, are determined.

**Authors:**Pineda-Villavicencio, Guillermo , Ugon, Julien , Yost, David**Date:**2018**Type:**Text , Journal article**Relation:**SIAM Journal on Discrete Mathematics Vol. 32, no. 3 (2018), p. 2011-2046, http://purl.org/au-research/grants/arc/DP180100602**Full Text:****Reviewed:****Description:**We define the excess degree \xi (P) of a d-polytope P as 2f1 - df0, where f0 and f1 denote the number of vertices and edges, respectively. This parameter measures how much P deviates from being simple. It turns out that the excess degree of a d-polytope does not take every natural number: the smallest possible values are 0 and d - 2, and the value d - 1 only occurs when d = 3 or 5. On the other hand, for fixed d, the number of values not taken by the excess degree is finite if d is odd, and the number of even values not taken by the excess degree is finite if d is even. The excess degree is then applied in three different settings. First, it is used to show that polytopes with small excess (i.e., \xi (P) < d) have a very particular structure: provided d ot = 5, either there is a unique nonsimple vertex, or every nonsimple vertex has degree d + 1. This implies that such polytopes behave in a similar manner to simple polytopes in terms of Minkowski decomposability: they are either decomposable or pyramidal, and their duals are always indecomposable. Second, we characterize completely the decomposable d-polytopes with 2d + 1 vertices (up to combinatorial equivalence). Third, all pairs (f0, f1), for which there exists a 5-polytope with f0 vertices and f1 edges, are determined.

Twisted sums with C(K) spaces

- Cabello Sanchez, Felix, Castillo, Jesus, Kalton, Nigel, Yost, David

**Authors:**Cabello Sanchez, Felix , Castillo, Jesus , Kalton, Nigel , Yost, David**Date:**2003**Type:**Text , Journal article**Relation:**Transactions of the American Mathematical Society Vol. 355, no. (2003), p. 4523-4541**Full Text:****Reviewed:****Description:**If X is a separable Banach space, we consider the existence of non-trivial twisted sums 0 -->**Description:**C1**Description:**2003002201

**Authors:**Cabello Sanchez, Felix , Castillo, Jesus , Kalton, Nigel , Yost, David**Date:**2003**Type:**Text , Journal article**Relation:**Transactions of the American Mathematical Society Vol. 355, no. (2003), p. 4523-4541**Full Text:****Reviewed:****Description:**If X is a separable Banach space, we consider the existence of non-trivial twisted sums 0 -->**Description:**C1**Description:**2003002201

Uniformly non-hexagonal Banach spaces

**Authors:**Yost, David**Date:**2007**Type:**Text , Conference paper**Relation:**Paper presented at 8th International Conference on Fixed Point Theory and its Applications, ICFPTA2007, Chiang Mai, Thailand : 16th-22nd July 2007**Full Text:**false**Description:**2003006614

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