Nonperiodicity implies unique composition for self-similar translationally finite Tilings

Let be a translationally finite self-similar tiling of R ^d . We prove that if is nonperiodic, then it has the unique composition property. More generally, has the unique composition property modulo the group of its translation symmetries. <lsiheader> <onlinepub>7 August, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>20n2p265.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>no <sectionname> </lsiheader> Received August 7, 1996, and in revised form December 18, 1996.     

A Generalization of the Erdos - Szekeres Theorem to Disjoint Convex Sets

Let F denote a family of pairwise disjoint convex sets in the plane. F is said to be in convex position if none of its members is contained in the convex hull of the union of the others. For any fixed k≥ 3 , we estimate P _k (n) , the maximum size of a family F with the property that any k members of F are in convex position, but no n are. In particular, for k=3 , we improve the triply exponential upper bound of T. Bisztriczky and G. Fejes Tóth by showing that P ₃ (n) < 16 ⁿ . <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p437.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received March 27, 1997, and in revised form July 10, 1997.     

Improved Bounds for Planar k -Sets and Related Problems

We prove an O(n(k+1) ^1/3 ) upper bound for planar k -sets. This is the first considerable improvement on this bound after its early solution approximately 27 years ago. Our proof technique also applies to improve the current bounds on the combinatorial complexities of k -levels in the arrangement of line segments, k convex polygons in the union of n lines, parametric minimum spanning trees, and parametric matroids in general. <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p373.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received May 31, 1997, and in revised form June 30, 1997.     

Isosceles Planar Subsets

A finite planar set is k -isosceles for k ≥ 3 if every k -point subset of the set contains a point equidistant from two others. There are three nonsimilar 3-isosceles sets with five points and one with six points. Eleven 4-isosceles sets with eight points are noted, and it is conjectured that no 4-isosceles set has nine points. Exactly one 4-isosceles 8-set has four points on a line, and every 4-isosceles set that includes the vertices of a square has fewer than eight points. <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p391.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received February 1, 1997, and in revised form June 24, 1997.     

On Point Sets with Many Unit Distances in Few Directions

We study the problem of the maximum number of unit distances among n points in the plane, under the additional restriction that we count only those unit distances that occur in a fixed set of k directions, taking the maximum over all sets of n points and all sets of k directions. We prove that, for fixed k and sufficiently large n > n ₀ (k) , the extremal sets are essentially sections of lattices, bounded by edges parallel to the k directions and of equal length. <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p355.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received January 10, 1997, and in revised form May 16, 1997.     

Canonical Theorems for Convex Sets

Let F be a family of pairwise disjoint compact convex sets in the plane such that none of them is contained in the convex hull of two others, and let r be a positive integer. We show that F has r disjoint ⌊ c _r n⌋ -membered subfamilies F _i (1 ≤ i ≤ r) such that no matter how we pick one element F _i from each F _i , they are in convex position, i.e., every F _i appears on the boundary of the convex hull of ⋃ _i=1 ^r F _i . (Here c _r is a positive constant depending only on r .) This generalizes and sharpens some results of Erdős and Szekeres, Bisztriczky and Fejes Tóth, Bárány and Valtr, and others. <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p427.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received April 30, 1997, and in revised form August 5, 1997.     

On Levels in Arrangements of Lines, Segments, Planes, and Triangles%

We consider the problem of bounding the complexity of the k th level in an arrangement of n curves or surfaces, a problem dual to, and an extension of, the well-known k-set problem. Among other results, we prove a new bound, O(nk ^5/3 ) , on the complexity of the k th level in an arrangement of n planes in R ³ , or on the number of k -sets in a set of n points in three dimensions, and we show that the complexity of the k th level in an arrangement of n line segments in the plane is , and that the complexity of the k th level in an arrangement of n triangles in 3-space is O(n ² k ^5/6 α(n/k)) . <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p315.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received February 7, 1997, and in revised form May 15, 1997, and August 30, 1997.     

Finding Convex Sets Among Points in the Plane

Let g(n) denote the least value such that any g(n) points in the plane in general position contain the vertices of a convex n -gon. In 1935, Erdős and Szekeres showed that g(n) exists, and they obtained the bounds Chung and Graham have recently improved the upper bound by 1; the first improvement since the original Erdős—Szekeres paper. We show that <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p405.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received January 1, 1997, and in revised form June 6, 1997.     

Note on the Erdos - Szekeres Theorem

Let g(n) denote the least integer such that among any g(n) points in general position in the plane there are always n in convex position. In 1935, P. Erdős and G. Szekeres showed that g(n) exists and . Recently, the upper bound has been slightly improved by Chung and Graham and by Kleitman and Pachter. In this paper we further improve the upper bound to <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p457.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received July 1, 1997, and in revised form July 14, 1997.     

A special case of mahler’s conjecture

A special case of Mahler's conjecture on the volume-product of symmetric convex bodies in n -dimensional Euclidean space is treated here. This is the case of polytopes with at most 2n+2 vertices (or facets). Mahler's conjecture is proved in this case for n≤ 8 and the minimal bodies are characterized. <lsiheader> <onlinepub>7 August, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>20n2p163.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>no <sectionname> </lsiheader> Received May 28, 1996, and in revised form November 7, 1996.     

Forced Convex n -Gons in the Plane

In a seminal paper from 1935, Erdős and Szekeres showed that for each n there exists a least value g(n) such that any subset of g(n) points in the plane in general position must always contain the vertices of a convex n -gon. In particular, they obtained the bounds which have stood unchanged since then. In this paper we remove the +1 from the upper bound for n ≥ 4 . <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p367.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received January 1, 1997, and in revised form June 6, 1997.     

Exponential Lower Bound for the Translative Kissing Numbers of d -Dimensional Convex Bodies

The translative kissing number H(K) of a d -dimensional convex body K is the maximum number of mutually nonoverlapping translates of K which touch K . In this paper we show that there exists an absolute constant c > 0 such that H(K)≥ 2 ^cd for every positive integer d and every d -dimensional convex body K . We also prove a generalization of this result for pairs of centrally symmetric convex bodies. <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p447.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received February 18, 1997, and in revised form April 15, 1997.     

Two finiteness theorems for periodic tilings of d-dimensional euclidean space

Consider the d -dimensional euclidean space E ^d . Two main results are presented: First, for any N∈ N, the number of types of periodic equivariant tilings that have precisely N orbits of (2,4,6, . . . ) -flags with respect to the symmetry group Γ , is finite. Second, for any N∈ N, the number of types of convex, periodic equivariant tilings that have precisely N orbits of tiles with respect to the symmetry group Γ , is finite. The former result (and some generalizations) is proved combinatorially, using Delaney symbols, whereas the proof of the latter result is based on both geometric arguments and Delaney symbols. <lsiheader> <onlinepub>7 August, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>20n2p143.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>no <sectionname> </lsiheader> Received September 5, 1996, and in revised form January 6, 1997.     

Rectification Principles in Additive Number Theory

We consider two general principles which allow us to reduce certain additive problems for residue classes modulo a prime to the corresponding problems for integers. <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p343.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received January 21, 1997, and in revised form April 9, 1997.     

A Combinatorial Problem on Polynomials

Problems and results on polynomials of two variables which take few distinct values on finite Cartesian products are considered. The methods we use come from combinatorial geometry. <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p383.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received January 6, 1997, and in revised form June 13, 1997.     

Tiling groups: New applications in the triangular lattice

We first give a new presentation of an algorithm, from W. Thurston, to tile polygons with ``calissons' (i.e., lozenges formed from two cells of the triangular lattice Λ ). Afterward, we use a similar method to get a linear algorithm to tile polygons with m -leaning bars (parallelograms of length m formed from 2m cells of Λ ) and equilateral triangles (whose sides have length m ) and we produce a quadratic algorithm to tile polygons with m -leaning bars. <lsiheader> <onlinepub>7 August, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>20n2p189.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>no <sectionname> </lsiheader> Received July 3, 1996, and in revised form May 14, 1997.     

On Geometric Graphs with No k Pairwise Parallel Edges

A geometric graph is a graph G=(V,E) drawn in the plane so that the vertex set V consists of points in general position and the edge set E consists of straight-line segments between points of V . Two edges of a geometric graph are said to be parallel if they are opposite sides of a convex quadrilateral. In this paper we show that, for any fixed k ≥ 3 , any geometric graph on n vertices with no k pairwise parallel edges contains at most O(n) edges, and any geometric graph on n vertices with no k pairwise crossing edges contains at most O(n log n) edges. We also prove a conjecture by Kupitz that any geometric graph on n vertices with no pair of parallel edges contains at most 2n-2 edges. <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p461.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received January 27, 1997, and in revised form March 4, 1997, and June 16, 1997.     

Covering the plane with copies of a convex disk

We prove that for every convex disk in the plane there exists a double-lattice covering of the plane with copies of with density ≤ 1.2281772 . This improves the best previously known upper bound ≤ 8/(3+2\sqrt{3}) 1.2376043 , due to Kuperberg, but it is still far from the conjectured value . <lsiheader> <onlinepub>7 August, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>20n2p251.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>no <sectionname> </lsiheader> Received June 1, 1996, and in revised form January 24, 1997.     

On Geometric Graphs with No Two Edges in Convex Position

A geometric graph is a graph G=G(V,E) drawn in the plane, where its vertex set V is a set of points in general position and its edge set E consists of straight segments whose endpoints belong to V . Two edges of a geometric graph are in convex position if they are disjoint edges of a convex quadrilateral. It is proved here that a geometric graph with n vertices and no edges in convex position contains at most 2n-1 edges. This almost solves a conjecture of Kupitz. The proof relies on a projection method (which may have other applications) and on a simple result of Davenport—Schinzel sequences of order 2. <lsiheader> <onlinepub>26 June, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>19n3p399.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>yes <sectionname> </lsiheader> Received December 18, 1995, and in revised form June 17, 1997.     

On the independence number of minimum distance graphs

Let F=F(n) denote the largest number such that any set of n points in the plane with minimum distance 1 has at least F elements, no two of which are at unit distance. Improving a result by Pollack, we show that F(n)≥ (9/35)n . We also give an O(n log n) time algorithm for selecting at least (9/35)n elements in a set of n points with minimum distance 1 so that no two selected points are at distance 1. <lsiheader> <onlinepub>7 August, 1998 <editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; <pdfname>20n2p179.pdf <pdfexist>yes <htmlexist>no <htmlfexist>no <texexist>no <sectionname> </lsiheader> Received June 12, 1996, and in revised form April 22, 1997.