From: Tony Smith 17 Feb 2003 Subject: magic triangle Predrag, my curiosity prompts me to ask about the magic triangle that you describe in Chapter 21 Exceptional Magic of your Group Theory web book. I see a very similar Magic Triangle in the paper of Pierre Deligne and Benedict Gross on the web at http://abel.math.harvard.edu/~gross/preprints/Exx.pdf Your paper and theirs both refer to P. Deligne, "La série exceptionelle de groupes de Lie, "C.R. Acad. Sci. Paris, Ser. I, 322, 321 (1996). Is that where the Magic Triangle was first discussed? Predrags answer: No. I introduced this Magic Triangle in my June 1977 Oxford preprint (available on this website) and published it in P. Cvitanovic', ``Negative dimensions and $E_7$ symmetry,'' Nucl. Phys. B 188, 373 (1981). See the ``Exceptional Magic" chapter in the webbok.