[1] Mathematical Sciences Department,
[2] IBM T.J. Watson Research Center,undefined
[3] Yorktown Heights,undefined
[4] NY 10598,undefined
[5] USA (e-mail: brucek@us.ibm.com),undefined
[6] Mathematics Institute,undefined
[7] University of Vienna,undefined
[8] Strudlhofgasse 4,undefined
[9] A-1090 Vienna,undefined
[10] Austria,undefined
[11] Erwin Schrödinger Institute for Mathematical Physics,undefined
[12] Boltzmanngasse 9,undefined
[13] A-1090 Vienna,undefined
[14] Austria (e-mail: klaus.schmidt@univie.ac.at),undefined