“…Certain issues as, e.g., a posteriori estimates, estimates of optimal order and regularity, fully discrete schemes with mesh modification, etc., have been extensively considered in the framework of Continuous and Discontinuous Galerkin methods, cf., e.g., [2,[7][8][9][10][11][12][13][14][15][16]. This is probably partly due to the fact that in principle space-time Galerkin methods provide freedom for (almost) arbitrary selection of the space time mesh, [11], and partly due merely to the fact that, as in the elliptic case, the properties of variational methods can be studied in an easier, more systematic and clearer way than properties of their pointwise counterparts, i.e., finite difference methods. Still many issues related to the above problems have to be investigated, mainly for nonlinear evolution PDE's.…”