title: Constraints and restraints in crystal structure analysis.
abstract: The widely used restraint-based approach to structural analysis using diffraction data is critiqued. The convenience of using rigid constraints, through the use of internal coordinates, is discussed.
authors.affiliation: Dipartimento di Chimica, Università di Salerno, I-84084 Fisciano (SA),  Italy.
authors.forename: Attilio
authors.initials: A
authors.lastname: Immirzi