L3A
       1. Definition: Torsion of a Curve Parametrized by Arc Length
       2. Derivation: Frenet Formula
 
L3B
       1. Definition: Normal Plane and Rectifying Plane
       2. Example: Helix
 
L3C
       1. Theorem: A Curve with Positive Curvature Is a Plane Curve
           if and only if Its Torsion Is Identically Zero