Order of consideration

Case

First

Second

Third

1

$z_1\left(x\right)$

$z_2\left(x\right)$

$z_3\left(x\right)$

2

$z_2\left(x\right)$

$z_1\left(x\right)$

$z_3\left(x\right)$

3

$z_1\left(x\right)$

$z_3\left(x\right)$

$z_2\left(x\right)$

4

$z_2\left(x\right)$

$z_3\left(x\right)$

$z_1\left(x\right)$

5

$z_3\left(x\right)$

$z_1\left(x\right)$

$z_2\left(x\right)$

6

$z_3\left(x\right)$

$z_2\left(x\right)$

$z_1\left(x\right)$