### Building a csg node ( Tut10.rt )

CSG stands for constructive solid geometry.

In tut10.rt you can see, from left to right the subtraction, the union and the intersection between two spheres.

You must give the two objects, like attributes :first and second. This attribute values can be also other csg node.

The material is not needed, csg node use the material of the associate objects.

Remember : objects in csg node must be always closed.

Look at file tut10.rt for an example of all tree case.