| http://www.wikidata.org/prop/statement/P2559
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A first-order class in Wikidata, e.g., wat … A first-order class in Wikidata, e.g., watercraft (Q1229765), bridge (Q12280), or human (Q5), is a class none of whose instances can be classes. Class that are a subclass of (P279) another class that is a first-order class are implicitly a first-order class, e.g., submarine (Q2811) is implicitly a first order class because it is a subclass of (P279) of (a subclass of) watercraft (Q1229765). There are many classes in Wikidata whose instances cannot be classes. It is only necessary to state that such a class is an instance of (P31) first-order class (Q104086571) to emphasize this point, particularly to distinguish it from a related second-order class such as to distinguish between watercraft (Q1229765) and watercraft type (Q16335899). Before stating that a class is an instance of (P31) first-order class (Q104086571) check that it is actually a first-order class, i.e., that it cannot have any instances that are classes.annot have any instances that are classes.
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