👉 In mathematics, an extension is a relation between two sets that includes all elements of one set in the set of the other. For example, if we have two sets A and B, then the extension of A to B, denoted by A ∪ B, consists of all elements from both A and B. The term "extensible" refers to a property where the relation being extended is able to include or extend any element in its set. In other words, if an element x exists
