L23A
       1. Derivation: Equations of Weingarten
 
L23B
       1. Derivation: Equations of Weingarten (cont.)
       2. Gauss Curvature in terms of the First and Second Fundamental Form
 
L23C
       1. Mean Curvature in terms of the First and Second
           Fundamental Form
       2. Principal Curvatures in terms of the First and Second
           Fundamental Form
       3. Proposition: Smoothness of Gauss Curvature, Mean
           Curvature and Principal Curvatures