Why singleton set is open in R?

In the standard topology on (\mathbb{R}), a singleton set, such as ({a}), is not considered open. An open set is defined as one that contains a neighborhood around each of its points, meaning for any point (x) in the set, there exists an interval ((x - \epsilon, x + \epsilon)) that is entirely contained within the set. Since a singleton set contains only the point (a) and does not include any interval around it, it does not satisfy the criteria for being open in (\mathbb{R}).