L19_A
         1. Example: The Normal Curvature and the Geodesic
             Curvature of the Circle on the Elliptic Parabolic
         2. Lemma: The Differentiable Extension of a
             Determination

L19_B
         1. Lemma: Relation between the Covariant Derivative of
             Two Unit Vector Fields and the Variation of the Angle
             That They Form
         2. Note: The Geodesic Curvature Is the Rate of Change
             of the Angle That the Tangent to the Curve Makes
             with a Parallel Vector Field 

         3. Proposition: An Expression for the Algebraic Value in
             Terms of the First Fundamental Form and the
             Variation of the Angle

L19_C
         1. Proposition: An Expression for the Algebraic Value in
             Terms of the First    Fundamental Form and the
             Variation of the Angle (cont.)