.
                
                                      P
                           s       s   y        s
                       y           c   h           y
                    c                o                 c
                   h                P                  h
                  o                  y                   o
                  P             c       h               P
                 s             o          P              s
                  y              s   ­   y               y
                    c                c                  c
                       h             h             h
                               o      o      o