PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX : <http://purl.org/net/schemarama#>
CONSTRUCT
{
  [] a :Warning;
    :message 'Resource [1] is preferred symbolic label for two separately identified concepts [2][3] in scheme [4] - are these concepts the same?.';
    :implicated ( ?l ?x ?y ?s );
  .
}
WHERE
{
  ?x skos:prefSymbol ?l; skos:inScheme ?s.
  ?y skos:prefSymbol ?l; skos:inScheme ?s.
  FILTER ( ?x != ?y )
}