c = Curve(f(t), g(t), t, start, end) : the command for constructing parametric curves with t.[br]u = Vector(A) : the position vector of the point A.[br]v = Vector(A, B) : the directed segment with the initial point A and the target point B.[br]D = C + u : D is the point moved from C with the moving vector u.[br]Vector[C, C+u] : C is the initial point and C+u is the target point.