In 1708, Bibiena was called to Barcelona to organize the decorations in connection with the wedding festivities of the future Holy Roman emperor Charles VI . In his decorations for the theatre and festivities, Bibliena replaced the central ( vertical ) axis with a diagonal axis, introducing an angular perspective along the diagonal.
12.
Note that for the symmetry group of a " square ", an uneven permutation of vertices does " not " correspond to taking a mirror image, but to operations not allowed for " rectangles ", i . e . 90?rotation and applying a diagonal axis of reflection.
