(Solved):
Is \( \{1\} \) open, closed, both, or neither in \( \left(\mathbb{R}, d^{E}\r ...
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Is \( \{1\} \) open, closed, both, or neither in \( \left(\mathbb{R}, d^{E}\right) \) (Euclidean metric)? How about in \( \left(\mathbb{R}, d^{D}\right) \) (discrete metric)? Explain.