Date: 2024-05-19 | Article ID: 69958 |

If X and Y are topological spaces and f is a map from X to Y, then the **homotopy class** [f] is the set of all maps from X to Y that are **homotopic** to f, which roughly means they can be continuously morphed to f. The **(free) homotopy set** [X,Y] is the set whose elements are homotopy classes of maps from X to Y. The **based homotopy set** is defined similarly, but using only homotopies that preserve a designated basepoint in X and in Y. The study of homotopy sets is a prominent part of the study of topology. Homotopy groups (article 61813) and cohomology groups (article 28539) may both be expressed as special families of homotopy sets equipped with a natural group structure. This article gathers some results about homotopy sets, with special attention given to the example [T^{3},SU(k)] where T^{3} is a 3-torus and SU(k) is a special unitary group.

**2024-05-19**(first version)

www.cphysics.org | © 2018-2024 Randy S For noncommercial use only |
updated 2024-07-11 |