only in taxon
only_in_taxon
U only_in_taxon T: U is a feature found in only in organisms of species of taxon T. The feature cannot be found in an organism of any species outside of (not subsumed by) that taxon. Down-propagates in U hierarchy, up-propagates in T hierarchy (species taxonomy). Implies applicable_to_taxon.
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.
never_outside_taxon
specific_to
Down-propagates. The original name for this in the paper is 'specific_to'. Applicable to genes because some genes are lost in sub-species (strains) of a species.
specific_to_taxon
RO:0002160
in taxon