L6_A

      1. Vector Field

      2. Trajectory of a Vector Field

      3. Examples: w=(x,y) and w=(y,-x) 

L6_B
      1. Theorem: Existence and Uniqueness of the Trajectory of
           a Vector Field

      2. Theorem: Existence of the Local Flow a Vector Field

L6_C
      1. Ruled Surface, Ruling and Directrix 

      2. Examples: Plane, Cylinder, Cone and Hyperboloid of
          Revolution