O: Yplung
    
\: w]

m: 
   1 UԦ\         YҨ   ->   L    ->  w]
   2 uC                 Y_Ҩ2   ->   w] 

  -- ]w ϼh, u,u,߽u,r,C

 { -- ť Ϊ 0 , uXw]
          pGƭ, Xw]ΦbΦmW[w
