🌙

☰

Retraction (topology)

In topology, a retraction is a continuous mapping from a topological space into a subspace that preserves the position of all points in that subspace. The subspace is then called a retract of the original space. A deformation retraction is a mapping that captures the idea of continuously shrinking a space into a subspace.

Definitions, Absolute neighborhood retract (ANR) & No-retraction theorem