Published online by Cambridge University Press: 30 March 2001
A modification of the method of geometric models is proposed and applied to the study of multiplicity functions of group extensions.
It is proved that, for some generic set of the automorphisms T of the Lebesgue space with respect to the standard topology, for any M\subseteq {\mathbb N} \cup \{\infty\}(1\in M) there exists a generic set of weakly mixing group extensions T' of transformation T with M(T')=M, where M(T) denotes the set of essential spectral multiplicities of the unitary operator corresponding to the transformation T.