L26A
        1. Proposition: A Regular Compact Connected Oriented
　　　  Surface Which Is　Not Homeomorphic to a Sphere Has Some Points
             Such That the Gauss　Curvature Is　Positive, Negative and Zero
        2. Proposition: Clairaut’s Theorem

L26B
         1. Proposition: Clairaut’s Theorem (cont.)

L26C
        1. Surface of Revolution and Hyperbolic Models