Suppose an ambiregnal taxon. If we provide a taxon concept entry to a name of the taxon under a Code (say ICBN and ICZN taxon concept entries for single taxon concept description), we need a way to specify an equivalence between these entries. Should it be covered by "is congruent to"? I think we need to use "is equivalent to" instead, because these entries designate an identical taxon concept by definition. Synonym is not applicable in this case because names under different Code can be synonym. Similer issue can happen with relationship between scientific name'd concept and common name'd concept; Japense taxonomists are keen to keep Japanese standard common names to be one-to-one mappable to scientific names. --JamesYtow

For ambiregnal relationships please see my comment for AmbiregnalTaxon. If people see the need for an additional equivalence type (that is different to any of the existing ones) we are happy to add it. We would really like to be able to allow taxonomists to establish any relationship they want. --RobertKukla 12/8/04