dl#properly_subsumes__PSB (pm#type,pm#type)  the '>' link in the FT notation
  subtype:  dl#properly_subsumes_leaf  the 2nd type is a leaf type properly subsumed by the 1st type
  equal:  pm#strict_subtype (pm)
  supertype:  pm#subtype__subtype_or_equal (pm#type,pm#type)  subtype links should actually be strict subtype links or not much checking can be done
     supertype:  pm#specializing_type (pm#type,?)
        supertype:  pm#relation_from_type (pm#type,*)  type of relations from a concept/relation type, i.e. in RDFS terminology, from a class or a property
           supertype:  pm#relation_from_collection (pm#collection,*)
              supertype:  pm#relation_from/to_thing_of_common_kind (*)  this type permits to categorize relations according to their signatures and hence offers (i) a concise way to set essential exclusion relations, and (ii) a systematic and easy-to-follow categorization
                 >part of:  pm#relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
              supertype:  pm#what_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
        supertype:  pm#partial_ordering_relation (?,?)  this category only serves structuration purposes: it is instance of pm#partial_ordering_relation_type which is not instance of pm#class_of_inheritable_relation_type
           supertype:  pm#reflexive_relation__reflexiverelation (?,?)  this category only serves structuration purposes: it is instance of pm#reflexive_relation_type which is not instance of pm#class_of_inheritable_relation_type
              supertype:  pm#binary_relation_with_particular_mathematical_property (?,?)
                 supertype:  pm#relation_with_particular_mathematical_property (*)
                    supertype:  pm#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:  pm#relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
           supertype:  pm#antisymmetric_relation__antisymmetricrelation (?,?)  this category only serves structuration purposes: it is instance of pm#antisymmetric_relation_type which is not instance of pm#class_of_inheritable_relation_type
              supertype:  pm#binary_relation_with_particular_mathematical_property (?,?)
           supertype:  pm#transitive_relation (?,?)  this category only serves structuration purposes: it is instance of pm#transitive_relation_type which is not instance of pm#class_of_inheritable_relation_type
              supertype:  pm#binary_relation_with_particular_mathematical_property (?,?)