    |           .    .| P
                    |             .  .|
                    |                *|

      if UPLO = 'U', or

                            N
                   |*                |
                   |.  .             |
                   |.    .           | P
                   |*  . . *         |
         |CU  |    -------------------
         |----|  = |*  . . . *       |
         |U'AU|    |.          .     |
                   |.            .   |
                   |.               