2013/04/05 by Andrzej P. Kisielewicz, Kisielewicz, Andrzej P. · 1 citation
Mathematics · #52C22 #52C25 #Combinatorics (math.CO) #FOS: Mathematics #Metric Geometry (math.MG) #math.CO #math.MG #msc:52C22 #msc:52C25
paper · pdf · doi:10.48550/arxiv.1304.1639
31 pages, 12 figures
arxiv created 2014/12/29 · arxiv updated 2014/12/30
A cube tiling of Rd is a family of pairwise disjoint cubes [0,1)d+T=\[0,1)d+t:t∈ T\ such that \bigcupt∈ T([0,1)d+t)=Rd. Two cubes [0,1)d+t, [0,1)d+s are called a twin pair if their closures have a complete facet in common, that is if |tj-sj|=1 for some j∈ [d]=\1,..., d\ and ti=si for every i∈ [d]∖ \j\. In 1930, Keller conjectured that in every cube tiling of Rd there is a twin pair. Keller's conjecture is true for dimensions d≤ 6 and false for all dimensions d≥ 8. For d=7 the conjecture is still open. Let x∈ Rd, i∈ [d], and let L(T,x,i) be the set of all ith coordinates ti of vectors t∈ T such that ([0,1)d+t)∩ ([0,1]d+x)≠ ∅ and ti≤ xi. Let r-(T)=minx∈ Rd max1≤ i≤ d|L(T,x,i)| and r+(T)=maxx∈ Rd max1≤ i≤ d|L(T,x,i)|. It is known that Keller's conjecture is true in dimension seven for cube tilings [0,1)7+T for which r-(T)≤ 2. In the present paper we show that it is also true for d=7 if r+(T)≥ 6. Thus, if [0,1)d+T is a counterexample to Keller's conjecture in dimension seven, then r-(T),r+(T)∈ \3,4,5\.