The window "Domain" displays a domain as a
wireframe, a point (u0, v0) in the domain, and
the u-constant and
v-constant curves, called the u-coordinate and v-coordinate curves,
through that point in red and green, respectively.
The window "Surface X(u,v)" shows the torus of revolution X(u,v) for
given domain and the images of the point and the curves from the
It is possible to change u0, v0,
a, and b in the control window.