$$ D = \{ z \in \mathbb{C} \ : \ |z| < \frac{1}{2} \}$$
It seems a disc is open or closed whether it has a < or <= but I don't know how to prove this. All examples have slightly different proofs so I've got no clarity.
Thanks for your help.
$$ D = \{ z \in \mathbb{C} \ : \ |z| < \frac{1}{2} \}$$
It seems a disc is open or closed whether it has a < or <= but I don't know how to prove this. All examples have slightly different proofs so I've got no clarity.
Thanks for your help.