L2A
       1.Orientation Preserving and Orientation Reversing Map
       2. Proposition: The Gauss Map is Orientation Preserving
           at Elliptic Point and Orientation Reversing at Hyperbolic  Point 
 
L2B
       1. Proposition: Geometric Interpretation of Gauss Curvature 
 
L2C
       1. Proposition: Geometric Interpretation of Gauss Curvature (cont.)
       2. Examples: Sphere and Trough-Shaped Surface