(one grain boundary constitutes a perfect circular boundary for the domain into which objects are to be packed [@sadoc1]). Outwards packing begins with the first complete grain boundary $[13, 8, 13]$ with 13 heptagons, 8 hexagons and 13 pentagons. The core is bounded by the 8 pentagons of the (first) incomplete grain boundary $[3, 5, 8]$. It has three heptagons instead of the full eight. The additional pentagons (nearly) fulfill the topological requirement that a tiled circular domain should have a topological charge of six [@rivier3; @rivier2].

The tiling is a foam made of topological hexagons, pentagons and heptagons, joined generically at vertices of degree three. Non-generic vertices appear on the grain boundaries. There is local organization throughout: The spirals (whorls) of first neighbors around each point (parastichies) are labelled by successive Fibonacci numbers [@sadoc2].

But, unlike a foam, it is organized and encoded by a one-dimensional encoding of a spiral lattice [@koch1; @coxeter; @rothen]; this encoding is the sequence $c(s)$ of the number of sides $\{5,6,7\}$ of the Voronoi cells around successive points on the generative spiral. Consecutive cells along the generative spiral (except the first two) are not neighbors. The sequence $c(s)$ shows some structural patterns (grain boundaries) 