Dezhou Kong Lishan Liu Yonghong Wu Isotonicity of the Metric Projection and Complementarity Problems in Hilbert Spaces. 341-355 2017 175 J. Optim. Theory Appl. 2 https://doi.org/10.1007/s10957-017-1162-8 db/journals/jota/jota175.html#KongLW17a