A  |  B  |  C  |  D
-----+-----+-----+-----
  1  |  a  |  6  |  x
  2  |  b  |  7  |  y
  3  |  c  |  7  |  z
  4  |  d  |  6  |  x
  5  |  a  |  6  |  y
  6  |  b  |  7  |  z
  7  |  c  |  7  |  x
  8  |  d  |  6  |  y

A -> BCD
B -> C

ABCD -> ABCD

ABD  BC