6. A Few References ___________________ There is a flourishing community publishing and discussing "Geometric Algebra" --- the application of Clifford algebra to analytic geometry --- which rarely seems to make contact with the outside world, and expends much energy on recycling stale material. Below I've disinterred a selection of the worthwhile minority hidden among the dross [there goes my invited address down the tube!] Most of my material has surely been folk-lore for a century of more; but if I knew of a satisfactory account of such matters, I shouldn't have felt obliged to write these notes. Once again, any suggestions? Rafal Ablamowicz Structure of Spin Groups Associated with Degenerate Clifford Algebras Journal of Mathematical Physics vol.27, pp.1--6 (1986); "CLIFFORD" (Algebra package for Maple V) http://math.gannon.edu/rafal/cliff3/ [One of very few to tackle degenerate Cl(p,q,r); concerned with implementation for theoretical physics.] S. L. Altmann "Rotations and Quaternions and Double Groups" Oxford (1986) [Does what it says on the tin, after a traditional fashion; but somehow, the wood tends to get lost among the trees.] T. E. Cecil "Lie Sphere Geometry" Springer ed.1 (1992), ed.2 (2008) [Introductory chapters discuss Lie-sphere group.] J. L. Coolidge "A Treatise on the Circle and the Sphere" Clarendon Press (1916); Chelsea (1971) [Extensive, idiosyncratic account of XIX-century analytic Lie-sphere geometry in later chapters.] C. J. L. Doran, A. N. Lasenby et al www.mrao.cam.ac.uk/~Clifford/ [Cavendish geometric algebra site: papers, Cl(4,1) software for 3-space Moebius group.] Jean Gallier "Clifford Algebras, Clifford Groups, and a Generalization of the Quaternions: The Pin and Spin Groups" www.cis.upenn.edu/~jean/home.html (online May 2008) [Good compact online account of (Bott) algebraic structure of Cl(p,q).] David Hestenes et al http://ModelingNTS.la.asu.edu/GC_R&D.html [Early modern proselyte for geometric algebra, though uninterested in nuts-and-bolts; papers passim, some online.] Pertti Lounesto "Clifford Algebras and Spinors" Cambridge University Press (2001) http://www.helsinki.fi/~lounesto/CLICAL.htm [Much detail about spinors, ideal structure, representation theory; unclear to me how this relates to practicality.] H. Pottmann & S. Leopoldseder "Geometries for CAGD" in "Handbook of 3D Modeling" pp.43--73 Elsevier (2002); online at http://www.geometrie.tuwien.ac.at/geom/leopoldseder/geom4cagd.pdf [Pottman's group at Vienna on Laguerre geometry.] Ian R. Porteous "Clifford Algebras and the Classical Groups" Cambridge University Press (1995, 2000, 2009) [Impressively complete account of classical theory of Cl(p,q), with relation to classical Lie groups.] Jon M. Selig "Geometrical Methods for Robotics" Springer ed.1 (1996), ed.2 (2005) [Sole published account of a properly thought-out, working metrical algebra, Cl(0,3,1) for Euclidean solid geometry; better is Cl(3,0,1)?]