#A1 singularity#Bacharach#Brill#Brill;#Diesel#Klein#Kummer surface#Meissner#Rohn#asymptotic cone#asymptotic line#catenary#caustic#constant Gaussian curvature#constant curvature#constant mean curvature#constant width#cross-section#double point#ellipse#ellipsoid#elliptic integral#geodesic line#hyperboloid#lambda-convexity#lines of curvature#locus#minimal surface#movable#negative curvature#orientation#paraboloid#principal curvature#quadric#quatric#real double point#rulings#sphere#surface of revolution#three-axial