링크  http://ge.tt/9tN3zy9

CURVATURE OF CURVES AND SURFACES – A PARABOLIC APPROACH, ZVI HAR’EL 
http://www.math.technion.ac.il/~rl/docs/parabola.pdf
Gaussian Curvature∗ Com S 477/577
http://www.cs.iastate.edu/~cs577/handouts/gaussian-curvature.pdf