Relation pm#why_relation__whyrelation (*)
  subtype:  cause  consequence  method  goal  triggering_event  ending_event  precondition  postcondition  purpose
  supertype:  wh-/how_relation (*)  this type permits to categorize relations according to the usual who/what/why/where/when/how questions ; this is a traditional but very subjective and ineffective way of categorizing relations 
     >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type