Yuelong Tang & Yanping Chen. (2020). Recovery Type a Posteriori Error Estimates of Fully Discrete Finite Element Methods for General Convex Parabolic Optimal Control Problems.
            <i>Numerical Mathematics: Theory, Methods and Applications</i>. <i>5</i> (4).
            573-591.
         doi:10.4208/nmtma.2012.m1117