Chunmei Liu, Tianliang Hou and Yin Yang. (2019). Superconvergence of $H$<sup>1</sup>-Galerkin Mixed Finite Element Methods for Elliptic Optimal Control Problems.
            <i>East Asian Journal on Applied Mathematics</i>. <i>9</i> (1).
            87-101.
         doi:10.4208/eajam.150117.070618