Cellular decomposition

In geometric topology, a cellular decomposition G of a manifold M is a decomposition of M as the disjoint union of cells (spaces homeomorphic to n-balls Bⁿ).

The quotient space M/G has points that correspond to the cells of the decomposition. There is a natural map from M to M/G, which is given the quotient topology. A fundamental question is whether M is homeomorphic to M/G. Bing's dogbone space is an example with M (equal to R³) not homeomorphic to M/G.

Definition

Cellular decomposition of $X$ is an open cover ${\mathcal {E}}$ with a function ${\text{deg}}:{\mathcal {E}}\to \mathbb {Z}$ for which:

• Cells are disjoint: for any distinct $e,e'\in {\mathcal {E}}$, $e\cap e'=\varnothing$.
• No set gets mapped to a negative number: ${\text{deg}}^{-1}(\{j\in \mathbb {Z} \mid j\leq -1\})=\varnothing$.
• Cells look like balls: For any $n\in \mathbb {N} _{0}$ and for any $e\in {\text{deg}}^{-1}(n)$ there exists a continuous map $\phi :B^{n}\to X$ that is an isomorphism ${\text{int}}B^{n}\cong e$ and also $\phi (\partial B^{n})\subseteq \cup {\text{deg}}^{-1}(n-1)$.

A cell complex is a pair $(X,{\mathcal {E}})$ where $X$ is a topological space and ${\mathcal {E}}$ is a cellular decomposition of $X$.

See also

• CW complex

References

• Daverman, Robert J. (2007), Decompositions of manifolds, AMS Chelsea Publishing, Providence, RI, p. 22, arXiv:0903.3055, ISBN 978-0-8218-4372-7, MR 2341468