D(1, xx)=x.x
D(1, zx)=z.x+x.y
D(2, xxx)=xx.x
D(1, xy*x)=x.y*x
D(2, zxx)=zx.x
D(3, xxxx)=xxx.x
D(2, xxy*x)=xx.y*x
D(2, xy*xx)=xy*x.x
D(1, xy*y*x)=x.y*y*x
D(3, zxxx)=zxx.x
D(2, zxy*x)=zx.y*x
B(1,1)=3
B(2,2)=2
B(2,3)=1
B(3,3)=2
B(2,4)=1
B(3,4)=3
B(4,4)=2
    0   1   2   3   4
  +------------------
0 | 1   3   2   2   2
1 | -   -   1   3
2 | -   -   1
3 | -   -
