The geometric model for Dn-Dynkin diagram is explicitly constructed and associated generic singularities of tangent surfaces are classified up to local diffeomorphisms. We observe, as well as the triality in D4 case, the difference of the classification for D3;D4;D5 and Dn(n ・ 6), and a kind of stability of the classification in Dn for n ! 1. Also we present the classifications of singularities of tangent surfaces for the cases B3;A3 = D3;G2;C2 = B2 and A2 arising from D4 by the processes of foldings and removings.
Dn-geometry and singularities of tangent surfaces
RIMSKB_B55_67_87
(202.04KB)
