diff --git a/theorems/T000893.md b/theorems/T000893.md new file mode 100644 index 000000000..95be921d4 --- /dev/null +++ b/theorems/T000893.md @@ -0,0 +1,23 @@ +--- +uid: T000893 +if: + and: + - P000240: true + - P000242: true +then: + P000199: true +refs: + - wikipedia: Whitehead_theorem + name: Whitehead theorem on Wikipedia + - zb: "1044.55001" + name: Algebraic Topology (Hatcher) +--- + +The [Whitehead theorem](https://en.wikipedia.org/wiki/Whitehead_theorem) states that a +[weak homotopy equivalence](https://en.wikipedia.org/wiki/Weak_equivalence_(homotopy_theory)) +from one CW complex to another is a homotopy equivalence. +See Theorem 4.5 in {{zb:1044.55001}}. + +In particular, suppose $X$ is a {P240}. Let $Y$ be {S162} and let $f:X\to Y$ be the constant map to $Y$. +If $X$ is {P242}, the map $f$ is a weak homotopy equivalence. +Since {S162|P240}, the Whitehead theorem implies that $X$ is homotopy equivalent to $Y$; that is, $X$ is {P199}.