Iranian Mathematical Society (IMS) Bulletin of the Iranian Mathematical Society 1017-060X 37 No. 4 2011 12 15 On the Ishikawa iteration process in CAT(0) spaces185 197 en B. Panyanak T. Laokul 2010 01 14 Nonexpansive mappings fixed points $Delta-$convergence strong convergence CAT(0) spaces