Open disk
= Open disk
{title2=$B^2=\{v\in\mathbb R^2:|v|<1\}$}
The <open disk> is the interior of a planar <disk>. Any such <open disk> is <homeomorphic> to $\mathbb R^2$, and in particular is <contractible> and <simply connected>.
= Open disk
{title2=$B^2=\{v\in\mathbb R^2:|v|<1\}$}
The <open disk> is the interior of a planar <disk>. Any such <open disk> is <homeomorphic> to $\mathbb R^2$, and in particular is <contractible> and <simply connected>.