L12A
        1. Review: Isometry and Conformal
        2. Note: A Conformal Map Preserves the Angle between
            Two Tangent Vectors
        3. Proposition: A Parametrization Is Conformal if and only
            if It is Isothermal
        4. Theorem: Any Two Regular Surfaces Are Locally
             Conformal 

L12B
        1. Proposition: A Criterion for Local Conformal
        2. Stereographic Projection


L12C
        1. Stereographic Projection (cont.)