kif#nil  the list that has no items; the uniqueness of null_list follows from the extensionality of lists, i.e. the fact that two lists with the same items in the same order are identical
  equal:  sumo#null_list (pm)  rdf#nil (pm)
  type:  kif#null__null_list  type of empty lists

No statement uses or specializes sumo#null_list; click here to add one.