A general approach to phase relationships: the method of representations

A theory is described which, for any universal structure invariant or structure seminvariant, Φ, is able to arrange the set of reflexions in shells, each shell a subset of the succeeding one, with the property that Φ may be estimated in terms of the magnitudes constituting any shell. The theory uses the idea that numberless representations exist of any universal structure invariant or seminvariant, each of them able to contribute to the estimate of Φ.