The $0$-sphere[1] is the pointed set $\smash {\webleft (S^{0},0\webright )}$[2] consisting of:
- The Underlying Set. The set $S^{0}$ defined by
\[ S^{0} \mathrel {\smash {\overset {\mathclap {\scriptscriptstyle \text{def}}}=}}\webleft\{ 0,1\webright\} . \]
- The Basepoint. The element $0$ of $S^{0}$.