“…The lower order conforming stress spaces for 1 ≤ k ≤ n − 1 in [8,10,17] include some proper high order piecewise polynomials and they add to the difficulty of implementation. On the other hand, as mentioned in [23], since the conforming stress spaces in [8][9][10] involve vertex degrees of freedom, techniques like hybridization usually available for mixed methods are not available for these methods, as well as for those elements in [14,15,17]. Apart from the weakly symmetric mixed finite element methods [24][25][26][27], strongly symmetric nonconforming stress approximations are used to overcome these drawbacks, see [23,[28][29][30][31][32] for some nonconforming mixed elements on simplicial grids, and [33][34][35][36][37] on rectangular and cuboid grids.…”