Smooth model of Boy's surface

Smooth model of Boy's surface using CSG (Constructive solid geometry), a way to model objects through simple building blocks and simple operations. Boy's surface is a famous self-intersecting surface with many striking properties. Building blocks used here are planes, cylinders, tori and a sphere. To obtain this surface, operations consist in taking intersections, unions, differences and complements. The degree of smoothness attained here is the following : there is a tangent plane at every point and its direction varies with the point proportionally to the displacement.