Properly Discontinuous Action
In topology and related branches of mathematics, an action of a group G on a topological space X is called proper if the map from G×X to X×X taking (g,x) to (gx,x) is proper, and is called properly discontinuous if in addition G is discrete. There are several other similar but inequivalent properties of group actions that are often confused with properly discontinuous actions.
Read more about Properly Discontinuous Action: Properly Discontinuous Action, Similar Properties
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