What is the significance of the condition fz  0 in a region D?
If fz  0 in a region D, it implies that the complex function f is constant on that region.
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### Instruction:
What is the significance of the condition fz  0 in a region D?

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### Response:
If fz  0 in a region D, it implies that the complex function f is constant on that region.<|im_end|>