Relation sumo#related_external_concept (pm#string,?,sumo#language)  used to signify a three-place relation between a concept in an external knowledge source, a concept in the SUMO, and the name of the other knowledge source
  subtype: {sumo#synonymous_external_concept sumo#subsumed_external_concept sumo#subsuming_external_concept}
  related_to:  pm#related_to
  type:  pm#ternary_predicate_type__ternarypredicatetype  class of predicates that require exactly three arguments
  supertype:  pm#relation_from_string (pm#string,*)
     supertype:  pm#relation_from_description_content/medium/container (pm#description_content/medium/container,*)
        supertype:  pm#relation_from/to_thing_of_common_kind (*)  this type permits to categorize relations according to their signatures and hence offers (i) a concise way to set essential exclusion relations, and (ii) a systematic and easy-to-follow categorization
           >part of:  pm#relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type