query: SELECT ?item ?catcode ?catnum WHERE {
    ?item p:P528 ?catstmt.
    ?catstmt pq:P972 wd:Q106831415;
      ps:P528 ?catcode.
    BIND(REPLACE(?catcode, "[0-9]*", "") AS ?catletter) 
    BIND( xsd:integer(REPLACE(?catcode, "[a-zA-Z()/.-]", "")) AS ?catnum) 
    FILTER(?catletter >= "a" )
  }
  ORDER BY (?catnum)