Affiliation: | 1. Department Of Mathematics , University Of Haifa , 31905 Haifa, DB, Israel;2. Department Of Mathematics , The Technion-Israel Institute Of Technology , 32000 Haifa, Sr And Ajz, Israel E-mail: dbutnaru@mathcs2.haifa.ac.il;3. sreich@tx.technion.ac.il;4. ajzasl@tx.technion.ac.il |