|Similarity: conformity of one or more - but not all - properties of two or more objects.|
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Def Equinumerous/Frege/Meixner: f is a property that is equinumerous with the property g = Def for at least a binary relation R: 1. Every entity that has f, stands to exactly one entity, that has g, in the relation R
2. If entities that have f, are different, then also entities with g
3. reversal of 1: any entity that has g
Numbers: one can then non-circularly define numbers: x is a natural number = x Def is a finite number property (Anzahl-Eigenschaft)
Number/Meixner: when conceived as a property, they are untyped functions.
Einführung in die Ontologie Darmstadt 2004