“…They seem to be the first who were able to show that a conformal metric structure is actually implied as a consequence of symmetry and closure. These structures were subsequently discussed by numerous people, by 't Hooft [70], Harnett [18], and Obukhov & Tertychniy [50], amongst others, see also the references given there. These structures were subsequently discussed by numerous people, by 't Hooft [70], Harnett [18], and Obukhov & Tertychniy [50], amongst others, see also the references given there.…”