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2. Idem, British Patent l 195 871 (1968).
3. H. Hund, H. Schaefer and D. Bergner, German Patent 2 300 422 (1974).
4. S. Kotowski, unpublished results.
5. D. Bergner and J. W. K�hn- von Burgsdorff,Chem. Ins. Techn. 52 (1980) 429.