To create a three-dimensional curve that looks to one person like [math]y=f(x)[/math] in the [math]xy[/math]-plane and [math]y=g(x)[/math] to another person, use the parametric equation [code]Curve(t,(f(t)+g(t))/2,(g(t)-f(t))/2,t,a,b)[/code] where [math]a[/math] and [math]b[/math] are the starting and ending parameter values.[br][br]To see the effect, line up points [math]A[/math] and [math]B[/math] and points [math]A[/math] and [math]C[/math].