“…Many authors have developed mixed elements with weak symmetry, 2,6,26,28,27,24,8,9,17,20,15,19 which we will not pursue here. For nonconforming methods with strong symmetry, which is the subject of this paper, there have been several elements proposed for rectangular meshes, 29,30,21,12,23 but very little work on simplicial meshes. A two-dimensional nonconforming element of low degree was developed by two of the present authors.…”