Smooth model of Boy's surface

Smooth model of Boy's surface using Constructive Solid Geometry (CSG), 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 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.