👉 In mathematics, a retrusive set is a subset of a metric space that contains all its limit points. In other words, it is closed under accumulation and every point in the set has an accumulation point. A retrusive set can be defined as any subset of a metric space where each open ball centered at a point contains more than one point from the set. For example, the unit interval [0,1] with its usual topology is a retrusive set because it contains all its limit points
