Author(s): Mohab Abou-Zeid, Harald Dorn (Humboldt Univ. Berlin)
-- hep-th/0009231 was replaced with a revised version
on Thu, 2 Nov 2000 17:51:18 GMT (11kb) --
Paper: hep-th/0009231
Comments: typo in formula (25) corrected
Report-no: HUB-EP-00/34
URL: http://arXiv.org/abs/hep-th/0009231