Relation pm#relation_with_variable_arity (*)  this category only serves structuration purposes: it is instance of pm#variable_arity_relation_type which is not instance of pm#class_of_inheritable_relation_type; currently not specialized by the SUMO ternary relations since this seems useless (for now)
  exclusion:  pm#binary_relation  pm#ternary_relation  pm#quaternary_relation
  type:  pm#variable_arity_relation_type  class of relations that do not have a fixed number of arguments
  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