👉 Unextendibility, also known as the "unextendable" property or "non-extensional" property, is a condition that a concept (e.g., a set) must satisfy in order for it to be considered a proper mathematical object. This means that if a concept cannot be extended beyond its current boundaries, such as through addition or multiplication by an element of the concept, then it cannot be considered a valid mathematical object. For example, consider two sets A and B (where A is
