Postscriptum: M. C. Escher's drawings as an educational tool for general and special positions of symmetry in crystals and molecules

The concept of occupancy of general and special positions of symmetry by molecules in crystals and occupancy of chirotopic and achirotopic positions of local-site symmetry by atoms in molecules are interrelated and are illustrated by M.C. Escher's periodic drawings. These concepts have a great influence upon x-ray crystallographic structure elucidation, and on the complexity of solid-state CP-MAS NMR spectra, as well as on the complexity of multiplets in solution-state NMR spectroscopy due to magnetic non-equivalence.