“…In fact, when u is a regular solution to (1), it is known that the graph (x, Du(x, t)) evolves by the mean curvature flow and it is a Lagrangian submanifold in R n × R n with the standard symplectic structure, for each t (cf. [5,6]). For a smooth stationary solution to (1), the graph of its gradient is a Lagrangian submanifold with zero mean curvature in R 2n .…”