text: let Tetrahedron = function () {
      let _ = Object.create (Primitive);
  
      _.name = "tetrahedron";
  
      _.getShapeBuilder = function () {
          let builder = ShapeBuilder.new ();
          builder.addVertex([1, 1, 1]);
          builder.addVertex([-1, 1, -1]);
          builder.addVertex([-1, -1, 1]);
          builder.addVertex([1, -1, -1]);
  
          builder.addFace([0, 1, 2]);
          builder.addFace([1, 3, 2]);
          builder.addFace([2, 3, 0]);
          builder.addFace([3, 1, 0]);
  
          return builder;
      };
  
      return _;
  } ();
  