An affirmative answer to Panyanak and Suantai s open question on the viscosity approximation methods for a nonexpansive multivalued mapping in CAT(0) spaces

An affirmative answer to the open question raised by Panyanak and Suantai [B. Panyanak, S. Suantai, Fixed Point Theory Appl., 2015 (2015), 14 pages] is given. Our results also generalize the results of Panyanak and Suantai [B. Panyanak, S. Suantai, Fixed Point Theory Appl., 2015 (2015), 14 pages], Wangkeeree and Preechasilp [R. Wangkeeree, P. Preechasilp, J. Inequal. Appl., 2013 (2013), 15 pages], Dhompongsa et al. [S. Dhompongsa, A. Kaewkhao, B. Panyanak, Nonlinear Anal., 75 (2012), 459 ndash;468], and many others. Some related results in Rtrees are also proved.