The representation theory, proposed by Giacovazzo (1977,1980) allowed the derivation of powerful methods for estimating structure invariants (s.i.) and structure seminvariants (s.s.). The mathematical approach makes full use of the space group symmetry. SIR92 uses symmetry in a quite general way allowing the estimation and use of s.i. and s.s. in all the space groups. The range of options available to experienced crystallographers for choosing their own way of solving crystal structures is rather wide. However scientists untrained in direct methods or experienced people trustful in the SIR92 default mode often can solve crystal structures without personal intervention.
The setting up of the SIR program was initiated a few years ago, and is the work of several authors. The present version (SIR92) of the program is the third release which we consider suitable for distribution and includes several new features with respect to the previous version, SIR88. A general description of the SIR92 program is given, as well as a detailed synopsis of all the commands and their use.