Z = 1 - 1 + 1 - 1 + 1.....
Z' =0 +1 - 1 +1 - 1.....

Z+Z' => All but the 1st term cancel out, leaving just 1.
2Z = 1.
Z = 0.5

Or another way:

Z = 1 - 1 + 1 - 1 + 1.....
Z = 1 - 1 + 1 - 1 + 1.....

2Z = 2 - 2 + 2 - 2 + 2.....
So, 2Z is either 2 or 0; average 1.
2Z = 1.
Z = 0.5

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