a) $(\mathbb{R}^2,\Vert \cdot \Vert_2)$, $U=(0,1]\times(0,1]$
b) $(\mathbb{R}^2,\Vert \cdot \Vert_2)$, $U = \mathbb{R} \cap B(0,1) $
c) $(C[-1,-1],\Vert \cdot \Vert_2)$, $U = \mathbb{P}_{12}$
I know that for a), $cl(0,1)$ is $[0,1]$ does this mean the answer is $[0,1]\times[0,1]$?