We introduce matrix algebra of subsets in metric spaces and we apply it to improve results of Yamauchi and Davila regarding Asymptotic Property C. Here is a representative result: Suppose X is an ∞-pseudo-metric space and n ≥ 0 is an integer. The asymptotic dimension asdim(X) of X is at most n if and only if for any real number r > 0 and any integer m ≥ 1 there is an augmented m× (n + 1)-matrix M = [B|A] (that means B is a column-matrix and A is an m × n-matrix) of subspaces of X of scale-r-dimension 0 such that M ·∩ M T is bigger than or equal to the identity matrix and B(A, r) ·∩ B(A, r) T is a diagonal matrix.
IntroductionThis paper is devoted to decomposition complexity understood as any coarse invariant defined in terms of decomposing spaces into r-disjoint subsets. Historically, the first such invariant, namely asymptotic dimension, was introduced by Gromov for the purpose of studying groups using geometric methods (see [32]). In Ostrand ([26] or [27]) formulation (see [4]) it can be defined as follows:Definition 1.1. Suppose X is a metric space. The asymptotic dimension of X is at most n if, for every real number r > 0, there is a decomposition of X into a union of its subsets X 0 , . . . , X n such that each X i is the union of a uniformly bounded and r-disjoint family U i . That means there is a real number S > 0 with each member of U i being of diameter at most S and the distance between points belonging to different elements of U i is at least r.Since then several concepts related to asymptotic dimension were introduced by various authors. One can see them as a spectrum with asymptotic dimension being the strongest concept and weak coarse paracompactness being the weakest (see [7]). The concept closest to asymptotic dimension was introduced by Dranishnikov [9] under the name of Asymptotic Property C: Definition 1.2. Suppose X is a metric space. X has Asymptotic Property C if, for every sequence of real numbers r i > 0, there is a decomposition of X into a finite union of its subsets X 0 , . . . , X n for some natural n such that each X i is the union of a uniformly bounded and r i -disjoint family U i .