Figure 2.1.

Two different realizations of the code $\mathcal{C}$ in (1). In both cases, the ambient space is $X={\mathbb{R}}^2$. (a) The open realization in consists of six open half-disks (or half-spaces), with opposite pairs sharing their linear boundary components. Three-element codewords correspond to the six open “pie slices”, while two-element words lie in the boundaries between these. (b) The closed good realization consists of closed annular sections. Two-element codewords correspond to the interior of pairwise intersections, while three-element codewords arise from the 1-dimensional triple intersections.