Classifying Space
Any crossed module
has a classifying space BM with the property that its homotopy groups are Coker d, in dimension 1, Ker d in dimension 2, and 0 above 2. It is possible to describe conveniently the homotopy classes of maps from a CW-complex to BM. This allows one to prove that (pointed, weak) homotopy 2-types are completely described by crossed modules.
Read more about this topic: Crossed Module
Famous quotes containing the word space:
“Time in his little cinema of the heart
Giving a première to Hate and Pain;
And Space urbanely keeping us apart.”
—Philip Larkin (1922–1986)