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
  supertype:  pm#relation_from_string (pm)
  instance of:  pm#ternary_predicate_type (pm)
  related_to:  pm#related_to
  subtype:  sumo#synonymous_external_concept (pm#string,?,sumo#language)  the 2nd argument has the same meaning as the 1st in the language denoted by the 3rd argument
  subtype:  sumo#subsumed_external_concept (pm#string,?,sumo#language)  the 2nd argument is subsumed by the 1st in the language denoted by the 3rd argument
  subtype:  sumo#subsuming_external_concept (pm#string,?,sumo#language)  the 2nd argument subsumes the 1st in the language denoted by the 3rd argument