Graffiti it is a rapidly developing art form whose value is highly contested and reviled by many authorities while also subject to protection, sometimes within the same jurisdiction. Both "graffiti" and its occasional singular form "graffito" are from the Italian word "graffiato" ("scratched"). "Graffiti" is applied in art history to works of art produced by scratching a design into a surface. A related term is "sgraffito", which involves scratching through one layer of pigment to reveal another beneath it. This technique was primarily used by potters who would glaze their wares and then scratch a design into it. In ancient times
Singular point of a curve smooth function "h" so that the curve has the form "y"="h"("x") near the origin. Similarly, if "b"≠0 then there is a smooth function "k" so that the curve has the form "x"="k"("y") near the origin. In either case, there is a smooth map from R to the plane which defines the curve in the neighborhood of the origin. Note that at the origin so the curve is non-singular or "regular" at the origin if at least one of the partial derivatives of "f" is non-zero. The singular points are those points on the curve where both partial derivatives vanish, Assume