C 1 , C 2 , , C m

α 1 , α 2 , , α m

B’s level total sorted P × C

{ P 1 P 2 P n

{ b 11 , b 12 , , b 1 m b 21 , b 22 , , b 2 m b n 1 , b n 2 , , b n n

{ j = 1 m α j b 1 j = b 1 j = 1 m α j b 2 j = b 2 j = 1 m α j b n j = b n