with(plots):
p1:=plot3d(x^3-3*x*y+y^3, x=-1..2, y=-1..2, axes=boxed, style=patchnogrid):
p2:=implicitplot3d(x^2+y^2+z^2=.01, x=-.1.. .1, y=-.1 .. .1, z=-.1 .. .1, color=violet, style=patchnogrid):
p3:=implicitplot3d((x-1)^2+(y-1)^2+(z+1)^2=.01, x=.9 .. 1.1, y=.9 .. 1.1, z=-1.1 .. -.9, color=blue, style=patchnogrid):
display(p1,p2,p3);