Relation nsm#before (?,?)
  supertype:  pm#binary_relation (pm)  in WebKB, most relation types are binary and some have a variable number of arguments (as in KIF), hence this type is currently only specialized by types that I do not want to see as direct subtypes of pm#relation
  subtype:  pm#before (pm#time_measure,pm#time_measure)
  subtype:  pm#before_time (pm#situation,pm#time_measure)
  subtype:  pm#later_situation__latersituation (pm#situation,pm#situation)
     subtype:  pm#next_situation (pm#situation -> pm#situation)
        subtype:  pm#successor (pm#situation -> pm#situation)
     subtype:  pm#ending_situation__termination (pm#situation -> pm#situation)
     subtype:  pm#postcondition (pm#process,pm#situation)
     subtype:  pm#consequence (pm#situation,pm#situation)  see also rst#effect