The action by deck transformations of the fundamental group of a locally simply connected space on an covering space is wandering and free. Such actions can be characterized by the following property: every x ∈ X has a neighbourhood U such that g ⋅ U ∩ U = ∅ for every g ∈ G ∖ { e G }. Actions with this property are sometimes called freely discontinuous, and the largest subset on which the action is freely discontinuous is then called the free regular set.