A collection of collections and a specialization of type of stuff composed entirely of one element. Each instance of element is a specialization of stuff composed entirely of one element which is defined _only_ by the atomic composition of its instances -- neither the isotopic composition or physical state of the substances, nor any other additional feature, determines membership in an instance of element. All that matters is that the instances of that collection are entirely composed of atoms having a particular number of protons in each atomic nucleus. Thus, the collection carbon is an instance of element, but neither the collection diamond nor the collection graphite is (even though they are subcollections of carbon), because their members have additional qualifications.