Relation pm#when_relation (?,?)
  subtype: {pm#relation_to_time pm#relation_from_situation_to_situation pm#temporal_relation}
  supertype:  pm#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:  pm#relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type