PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX : <http://purl.org/net/schemarama#>
CONSTRUCT
{
  [] a :Error;
    :message 'Resource [1] is both preferred and alternative symbolic label for concept [2].';
    :implicated ( ?n ?x );
  .
}
WHERE
{
  ?x skos:prefSymbol ?n.
  ?x skos:altSymbol ?n.
}