User's guide to "Les belles surfaces":
This Windows program does not require installing. Just download and double click.
The program draws a sketch of a parametric surface, preferably smooth. The
hidden contours of the surface are drawn in grey, and the apparent contours in black. The self-intersections are
drawn in blue
1) The surface data is input in the menu "Surface", "Equation". It is given in parametric form, the options
"raccord en u" and "raccord en v" allow, for instance when drawing a torus, to avoid drawing the boundary of
the coordinate square.
Assuming the coordinate square is 0