deformation retract
英[ˌdi:fɔ:ˈmeɪʃən rɪˈtrækt]美[ˌdifɔrˈmeʃən rɪˈtrækt]
In topology, a branch of mathematics, a retraction, is a continuous mapping from the entire space into a subspace which preserves the position of all points in that subspace. A deformation retraction is a map which captures the idea of continuously shrinking a space into a subspace.