Function sumo#property_fn (agentive_physical_object -> set)  maps an agent to the set of objects owned by the agent
  type:  unary_function_type  class of functions requiring a single argument; if R is functional, then if R(x -> y) and P(x -> z) then y=z
  type:  total_valued_relation_type  when there exists an assignment for the last argument position of the relation given any assignment of values to every argument position except the last one; note that declaring a relation to be both a total_valued_relation and a single_valued_relation means that it is a total function
  supertype:  owner_of__ownerof (causal_entity,?)
     supertype:  attributive_relation__attributiverelation (*)  like pm#binary_relation, this type mostly exists to categorize what cannot be categorized elsewhere
        supertype:  relation_playing_a_special_role (*)  this type permits to categorize relations according to their roles ; this is a traditional but quite subjective way of categorizing relations
           >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type