A sequentially closed set is one that contains every limit of its convergent sequences. This is weaker than being a closed set in a general topological space, but the two conditions agree in metric spaces.
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In topology, a **closed set** is a fundamental concept related to the structure of a topological space. A subset \( C \) of a topological space \( X \) is called closed if it contains all its limit points. Here are some important properties and characteristics of closed sets: 1. **Complement**: A set is closed if its complement (with respect to the whole space \( X \)) is open.