code: function Tetrahedron(r) {
    r = r || 0.5;
  
    var s3 = Math.sqrt(3);
    var s6 = Math.sqrt(6);
  
    var vertices = [
      new Vec3( s3/3, -s6/3 * 0.333 + s6*0.025,    0),   //right
      new Vec3(-s3/6, -s6/3 * 0.333 + s6*0.025,  1/2),   //left front
      new Vec3(-s3/6, -s6/3 * 0.333 + s6*0.025, -1/2),   //left back
      new Vec3(    0,  s6/3 * 0.666 + s6*0.025,    0)    //top
    ];;
  
    vertices = vertices.map(function(v) { return v.normalize().scale(r); })
  
    var faces = [
      [0, 1, 2],
      [3, 1, 0],
      [3, 0, 2],
      [3, 2, 1]
    ];
  
    var edges = [
      [0, 1],
      [0, 2],
      [0, 3],
      [1, 2],
      [1, 3],
      [2, 3]
    ];
  
    Geometry.call(this, { vertices: vertices, faces: faces, edges: edges });
  }
docs: ### Tetrahedron ( r ) `r` - radius *{ Number = 0.5 }*