A cubic millimeter (10-9 m3) of condensed matter contains typically ∼1020 atoms, and a complete solution to the general structure problem requires finding ∼3 ×l020 atom coordinates. For crystals, long-range translational periodicity immensely simplifies the structure elucidation problem to something like a 101-102 problem (further reduced by the symmetry accompanying orientational order), because only the contents of the unit cell (< 100 atoms for most inorganic structures) and the unit cell geometry need be determined. Amorphous is the epithet traditionally bestowed on structures with neither orientation nor translational order, a more precise term for which is topologically disordered [1], A structural average for an amorphous solid can be established with a good many fewer than 1020 atoms, because many atom-atom correlations nevertheless exist in topologically-disordered structures due to bonding, packing and associated topological constraints. In fact, assemblies with less than 200 atoms can usually adequately represent characteristic structural topologies [1].