Mathematics of Computation, Vol. 71, No. 240 (Oct., 2002), pp. 1421-1430 (10 pages) Finite element derivative superconvergent points for harmonic functions under local rectangular mesh are ...
Transactions of the American Mathematical Society, Vol. 263, No. 2 (Feb., 1981), pp. 493-500 (8 pages) Let $\Delta'$ be the class of all derivatives. The main goal of ...