Relation pm#trichotomizing_relation_on_real_number (quantity,quantity)
  subtype:  less_than  greater_than  less_than_or_equal  greater_than_or_equal
  supertype:  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:  binary_relation_with_particular_mathematical_property (?,?)
        supertype:  relation_with_particular_mathematical_property (*)
           supertype:  relation_with_particular_property (*)  this rather fuzzy type permits to group categorization schemes less common than those covered by the previous sibling categories
              >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type