only in taxon lactation SubClassOf 'only in taxon' some 'Mammalia' x only in taxon y if and only if x is in taxon y, and there is no other organism z such that y!=z a and x is in taxon z. The original intent was to treat this as a macro that expands to 'in taxon' only ?Y - however, this is not necessary if we instead have supplemental axioms that state that each pair of sibling tax have a disjointness axiom using the 'in taxon' property - e.g. 'in taxon' some Eukaryota DisjointWith 'in taxon' some Eubacteria in taxon