  The present review presents the authors previous results on the topic from
the title in a new light. Most of the previous results were obtained using the
techniques of antilinear Hilbert-Schmidt mappings of one Hilbert pace into
another, which is unknown and unused in the literature. This, naturally,
diminished the impact of the results. In this article the results are derived
anew with standard techniques. The topics listed at the end of the
Introduction, are expounded in 9 theorems, 5 propositions etc. Partial scalar
product and partial trace methods are used throughout. Further relevant
research articles that are not reproduced in this review, are sketched in the
Concluding remarks.
