L21_A
1. Definition: Gauss Curvature and Mean Curvature
2. Definition: Elliptic, Hyperbolic, Planar and Parabolic Point
L21_B
1. Definition: Umbilical Point
2. Example: Study the Gauss Map on {2z=x^2＋y^2} at (0,0,0)
L21_C
1. Proposition: A Connected Surface with Every Point Being Umbilical
Point Is a Piece of Plane or Sphere
10610 池盷恩同學幾何筆記.pdf
