Relation pm#trichotomizing_relation (?,?)  this category only serves structuration purposes: it is instance of pm#trichotomizing_relation_type which is not instance of pm#class_of_inheritable_relation_type
  supertype:  pm#binary_relation_with_particular_mathematical_property
  instance of:  pm#trichotomizing_relation_type
  subtype:  pm#trichotomizing_relation_on_real_number (sumo#quantity,sumo#quantity)
     subtype:  sumo#less_than (sumo#quantity,sumo#quantity)
     subtype:  sumo#greater_than__greaterthan (sumo#quantity,sumo#quantity)
     subtype:  sumo#less_than_or_equal (sumo#quantity,sumo#quantity)
     subtype:  sumo#greater_than_or_equal (sumo#quantity,sumo#quantity)