“…In both cases the vector of the unknown functions (nodal displacement vector { }) consists of eighteen elements: displacements and in the and directions, respectively, of moving nodes 2, 3, 4, 5, and 6 and the nodal deformation angles Θ The order of the nodal displacement vector for the rigid-body motion { 0 } differs depending on the case considered. In (22) it consists of ten elements, that is, the displacements of moving nodes in the and direction, respectively, due to the rigid-body motion (i.e., all displacements are with the index 0):…”