1. Belg. Pat. 859 656 (1978) to M. R. Klotz.
2. Fr. Pat. 2 429 182 (1979) to M. Taramasso, G. Manara, V. Fattore and B. Notari.
3. Ger. Pat. 2 909 929 (1980) to L. Marosi, J. Stabenow and M. Schwarzmann.
4. U.S. Pat. 4 208 305 (1984) to H. W. Kouwenhoven and W. H. J. Stork.