query: SELECT
  	?item
  	(GROUP_CONCAT(DISTINCT(concat("\u007B\u007BP\u007C",strafter(str(?se),"/entity/"),"\u007D\u007D"));separator=", ") as ?seealso)
  WHERE
  {
  	?item wdt:P279 wd:Q21502402 . 
  	OPTIONAL { ?item wdt:P1659 ?se }
  }
  GROUP BY ?item