“A study of the symmetry of three-dimensional spaces is of great theoretical and practical significance, because symmetrical spaces include crystals (from which, of course, the majority of solids are formed), and all homogeneous fields without exception: electric, magnetic, gravitational, etc. A study of the structures of crystals is unthinkable without a knowledge of the laws governing symmetry of three-dimensional spaces” (from Shubnikov and Koptsik, 1974).