TransformMatrix -- Create a rotation matrix

i1 : a=Polygon{{[-1,0],[1,0.1],[1,-0.1]},"fill"=>"red"}

o1 = a

o1 : Polygon

i2 : gList(a,a++{TransformMatrix=>rotation(2*pi/3)})

o2 = GraphicsList{cache => CacheTable{}                                                }
                  Contents => {a, Polygon{cache => CacheTable{}                      }}
                                          PointList => {| -1 |, |  1 |, |  1  |}
                                                        |  0 |  | .1 |  | -.1 |
                                                        |  0 |  |  0 |  |  0  |
                                                        |  1 |  |  1 |  |  1  |
                                          style => MutableHashTable{...1...}
                                          TransformMatrix => | -.5     -.866025 0 0 |
                                                             | .866025 -.5      0 0 |
                                                             | 0       0        1 0 |
                                                             | 0       0        0 1 |
                  style => MutableHashTable{}

o2 : GraphicsList