Published online by Cambridge University Press: 24 October 2008
The complete (or “extended”) symmetry groups, investigated in Part I, are certain groups of orthogonal transformations, generated by reflections. Every such group has a subgroup of index two, consisting of those transformations which are of positive determinant (i.e., “movements” or “displacements”). The positive subgroup (in this sense) of [k1, k2, …, kn−1] is denoted by [k1, k2, …, kn−1]′, and is “the rotation group” (or, briefly, “the group”) of either of the regular polytopes {k1, k2, …, kn−1}, {kn−1, kn−2, …, k1}; e.g., [3, 4]′ is the octahedral group.
* Coxeter, and Todd, , Proc. Camb. Phil. Soc. 32 (1936), 194–200.CrossRefGoogle Scholar
† Part I, 194.
‡ Klein, F., Vorlesungen über das Ikosaeder (Leipzig, 1884), 16, 19.Google Scholar
§ Todd, J. A., Proc. Camb. Phil. Soc. 27 (1931), 218.Google Scholar Cf. Littlewood, D. E., Proc. London Math. Soc. (2), 32 (1930), 18, 14,Google Scholar where six generators are used.
∥ Todd, loc. cit. 228. Hereafter (as in Part I), we shall refer to that paper as G.S.R.P.
* Part I, 197.
† Artin, E., “Theorie der Zöpfe”, Abhandl. Math. Sem. Hamburg. Univ. 4 (1926), 52–54.Google Scholar Artin's definition is actually
for the symmetric group of degree n. ([3n−1] is the symmetric group of degree n + 1)
* Coxeter, , Journal London Math. Soc. 11 (1936), 151.Google Scholar There we showed that the relations
imply
whence
† Coxeter, loc. cit. 151–153.
* Todd, and Coxeter, , “A practical method for enumerating cosets of a finite abstract group”, Proc. Edinburgh Math. Soc. (2), 5 (1936), 31.CrossRefGoogle Scholar
† G.S.R.P. 226.
‡ Part I, 199. A printer's error should be corrected in the re-statement of this definition on the eighth line of p. 195.
§ Cf. Coxeter, , Proc. London Math. Soc. (2), 41 (1936), 289Google Scholar (6·8). We have changed S into S −1, for the sake of analogy with (12). The relation R 2m = 1 is clearly superfluous. When n is odd, these relations define the hyper-pyritohedral group [(3n−2)′, 4].
* Coxeter, loc. cit. 287 (5·9).
† G.S.R.P. 216, 225.
‡ G.S.R.P. 224, 217.
* Coxeter and Sinkov, “The groups determined by the relations
S l = T m = (S −1T −1ST)p = 1”,
Duke Math. Journal, 2 (1936), 68, 76.Google Scholar
† G.S.R.P. 229. The first sentence should read, “The group contains a sub-group of order two, generated by the central inversion; since this operation…”.
* Robinson, G. de B., “On the orthogonal groups in four dimensions”, Proc. Camb. Phil. Soc. 27 (1931), 43.CrossRefGoogle Scholar
† For the properties of the operation R 1R 2R 3R 4 (which is conjugate to R 1R 2R 4R 3), see G.S.R.P. 227, or Coxeter, Annals of Math. 35 (1934), 608 (vi). In the case of [[3, 3, 3]] and [[3, 3, 3]]′, R is of period 10, and R 5 is the central inversion.
‡ “The groups of the regular solids in n dimensions”, Proc. London Math. Soc. (2), 32 (1930), 12.Google Scholar This is essentially the same as the decomposition of an orthogonal substitution by Goursat, E., Ann. Sci. de l'Éc. Norm. Sup. (3), 6 (1889), 28.Google Scholar
§ Littlewood, loc. cit. 17.
* “Topologische Untersuchung der Diskontinuitätsbereiche endlicher Bewegungs-gruppen des dreidimensionalen sphärischen Raumes”, Math. Ann. 107 (1932), 582.Google Scholar
† The following considerations furnish an abstract proof for these results.
‡ Jhber. Deutsch. Math.-Vereinig. 41 (1931), II. Teil, 6, 7Google Scholar (Aufgabe 84).
§ G.S.R.P. 226.
∥ Coxeter, , Annals of Math. 35 (1934), 608CrossRefGoogle Scholar (vii). In G.S.R.P. 230, Todd expresses S as a permutation.
* The third analogous result is that two binary tetrahedral groups with a common central lead to the group [3, 4, 3]″, of order
† G. de B. Robinson, loc. cit.
‡ Coxeter, , Proc. London Math. Soc. (2), 38 (1935), 331.Google Scholar
§ Math. Ann. 104 (1930), 64.Google Scholar