L26_A
        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

L26_B
         1. Proposition: Clairaut’s Theorem (cont.)

L26_C
        1. Surface of Revolution and Hyperbolic Models