Annotated link http://www.diigo.com/bookmark/http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=PMARCW000006000001015002000001&idtype=cvips
S. Donaldson. (1999)cite arxiv:math/9911248Comment: 16 pages. Published copy, also available at http://www.maths.warwick.ac.uk/gt/GTMon2/paper4.abs.html.