+++            +++ sa
                          +   +          +   /
                         +     +        +     +
                        + xy  xr+      + xy    +
                        +   +---+      +   +   +
                        +   |   +      +       +
                         +  |yr+        +     +
                          + | +          +   \
                           +++            +++ ea

                                 CIRCLE