title: Theo Hahn (1928-2016).
authors.affiliation: Institut für Kristallographie, RWTH Aachen University, Jaegerstrasse 17-19, 52056 Aachen, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Klapper
keywords: International Tables for Crystallography; obituary; phase transitions; symmetry; tetrahedral framework structures; twinning