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Publication date 23/05/2014
Field of study Full text link A cube tiling of R d \mathbb{R}^d R d is a family of pairwise disjoint cubes
[ 0 , 1 ) d + T = { [ 0 , 1 ) d + t : t β T } [0,1)^d+T=\{[0,1)^d+t:t\in T\} [ 0 , 1 ) d + T = {[ 0 , 1 ) d + t : t β T } such that β t β T ( [ 0 , 1 ) d + t ) = R d \bigcup_{t\in
T}([0,1)^d+t)=\mathbb{R}^d β t β T β ([ 0 , 1 ) d + t ) = R d . Two cubes [ 0 , 1 ) d + t [0,1)^d+t [ 0 , 1 ) d + t , [ 0 , 1 ) d + s [0,1)^d+s [ 0 , 1 ) d + s are called a
twin pair if β£ t j β s j β£ = 1 |t_j-s_j|=1 β£ t j β β s j β β£ = 1 for some j β [ d ] = { 1 , β¦ , d } j\in [d]=\{1,\ldots, d\} j β [ d ] = { 1 , β¦ , d } and t i = s i t_i=s_i t i β = s i β
for every i β [ d ] β { j } i\in [d]\setminus \{j\} i β [ d ] β { j } . In 1930 1930 1930 , Keller conjectured that in
every cube tiling of R d \mathbb{R}^d R d there is a twin pair. Keller's conjecture
is true for dimensions d β€ 6 d\leq 6 d β€ 6 and false for all dimensions d β₯ 8 d\geq 8 d β₯ 8 . For
d = 7 d=7 d = 7 the conjecture is still open. Let x β R d x\in \mathbb{R}^d x β R d , i β [ d ] i\in [d] i β [ d ] , and
let L ( T , x , i ) L(T,x,i) L ( T , x , i ) be the set of all i i i th coordinates t i t_i t i β of vectors t β T t\in T t β T
such that ( [ 0 , 1 ) d + t ) β© ( [ 0 , 1 ] d + x ) β β
([0,1)^d+t)\cap ([0,1]^d+x)\neq \emptyset ([ 0 , 1 ) d + t ) β© ([ 0 , 1 ] d + x ) ξ = β
and t i β€ x i t_i\leq x_i t i β β€ x i β . It is
known that if β£ L ( T , x , i ) β£ β€ 2 |L(T,x,i)|\leq 2 β£ L ( T , x , i ) β£ β€ 2 for some x β R 7 x\in \mathbb{R}^7 x β R 7 and every i β [ 7 ] i\in
[7] i β [ 7 ] or β£ L ( T , x , i ) β£ β₯ 6 |L(T,x,i)|\geq 6 β£ L ( T , x , i ) β£ β₯ 6 for some x β R 7 x\in \mathbb{R}^7 x β R 7 and i β [ 7 ] i\in [7] i β [ 7 ] , then
Keller's conjecture is true for d = 7 d=7 d = 7 . In the present paper we show that it is
also true for d = 7 d=7 d = 7 if β£ L ( T , x , i ) β£ = 5 |L(T,x,i)|=5 β£ L ( T , x , i ) β£ = 5 for some x β R 7 x\in \mathbb{R}^7 x β R 7 and i β [ 7 ] i\in
[7] i β [ 7 ] . Thus, if there is a counterexample to Keller's conjecture in dimension
seven, then β£ L ( T , x , i ) β£ β { 3 , 4 } |L(T,x,i)|\in \{3,4\} β£ L ( T , x , i ) β£ β { 3 , 4 } for some x β R 7 x\in \mathbb{R}^7 x β R 7 and i β [ 7 ] i\in
[7] i β [ 7 ] .Comment: 37 pages, 7 figures. arXiv admin note: substantial text overlap with
arXiv:1304.163
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Publication date 01/01/1989
Field of study Get PDF
Publication venue
Publication date 30/10/2023
Field of study Full text link Two d d d -dimensional simplices in R d R^d R d are neighborly if its intersection is
a ( d β 1 ) (d-1) ( d β 1 ) -dimensional set. A family of d d d -dimensional simplices in R d R^d R d is
called neighborly if every two simplices of the family are neighborly. Let
S d S_d S d β be the maximal cardinality of a neighborly family of d d d -dimensional
simplices in R d R^d R d . Based on the structure of some codes V β { 0 , 1 , β } n V\subset \{0,1,*\}^n V β { 0 , 1 , β } n
it is shown that lim β‘ d β β ( 2 d + 1 β S d ) = β \lim_{d\rightarrow \infty}(2^{d+1}-S_d)=\infty lim d β β β ( 2 d + 1 β S d β ) = β . Moreover, a
result on the structure of codes V β { 0 , 1 , β } n V\subset \{0,1,*\}^n V β { 0 , 1 , β } n is given