Relation sumo#related_external_concept (string,?,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: {synonymous_external_concept subsumed_external_concept subsuming_external_concept}
  related_to:  related_to
  type:  ternary_predicate_type__ternarypredicatetype  class of predicates that require exactly three arguments
  supertype:  relation_from_string (string,*)
     supertype:  relation_from_description_content/medium/container (description_content/medium/container,*)
        supertype:  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:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type