x y y z x z y z
x y x z y z
x y y z x y z y y z
(3.17)
We first try
x y y z x y y z, (3.18)
where the interchange of both and .
Next we try
x y y z
x z z y
x z y z x z z y
(3.19)
where z and y can be used interchangeably, by Definition 2.3( BCL -2).
By Definition 3.1(D1), in the case that
x y y z 1. (3.20)
By Theorem 2.3 and Theorem 2.4 we see that
1
1 1
x y x z z y
x z x y y z
x z x z
(3.21)
then 1 1, as required.